MariaDB MaxScale Configuration Guide

MariaDB MaxScale Configuration Guide


This document describes how to configure MariaDB MaxScale and presents some possible usage scenarios. MariaDB MaxScale is designed with flexibility in mind, and consists of an event processing core with various support functions and plugin modules that tailor the behavior of the program.



Word Description
connection routing Connection routing is a method of handling requests in which MariaDB MaxScale will accept connections from a client and route data on that connection to a single database using a single connection. Connection based routing will not examine individual requests on a connection and it will not move that connection once it is established.
statement routing Statement routing is a method of handling requests in which each request within a connection will be handled individually. Requests may be sent to one or more servers and connections may be dynamically added or removed from the session.
module A module is a separate code entity that may be loaded dynamically into MariaDB MaxScale to increase the available functionality. Modules are implemented as run-time loadable shared objects.
connection failover When a connection currently being used between MariaDB MaxScale and the database server fails a replacement will be automatically created to another server by MariaDB MaxScale without client intervention
backend database A term used to refer to a database that sits behind MariaDB MaxScale and is accessed by applications via MariaDB MaxScale.
REST API HTTP administrative interface



A server represents an individual database server to which a client can be connected via MariaDB MaxScale. The status of a server varies during the lifetime of the server and typically the status is updated by some monitor. However, it is also possible to update the status of a server manually.

Status Description
Running The server is running.
Master The server is the master.
Slave The server is a slave.
Draining The server is being drained. Existing connections can continue to be used, but no new connections will be created to the server. Typically this status bit is turned on manually using maxctrl, but a monitor may also turn it on.
Drained The server has been drained. The server was being drained and now the number of connections to the server has dropped to 0.
Auth Error The monitor cannot login and query the server due to insufficient privileges.
Maintenance The server is under maintenance. Typically this status bit is turned on manually using maxctrl, but it will also be turned on for a server that for some reason is blocking connections from MaxScale. When a server is in maintenace mode, no connections will be created to it and existing connections will be closed.
Slave of External Master The server is a slave of a master that is not being monitored.


A protocol module is responsible for the low-level communication between MaxScale and either clients of MaxScale or servers exposed by MaxScale. The most commonly used protocol modules are mariadbclient and mariadbbackend.

Protocol modules do not have sections of their own in the MaxScale configuration file, but are referred to from servers and listeners.


A monitor module is capable of monitoring the state of a particular kind of cluster and making that state available to the routers of MaxScale.

Examples of monitor modules are mariadbmon that is capable of monitoring a regular master-slave cluster and in addition of performing both switchover and failover, galeramon that is capable of monitoring a Galera cluster, csmon that is capable of monitoring a Columnstore cluster and clustrixmon that is capable of monitoring a Clustrix cluster.

Monitor modules have sections of their own in the MaxScale configuration file.


A filter module resides in front of routers in the request processing chain of MaxScale. That is, a filter will see a request before it reaches the router and before a response is sent back to the client. This allows filters to reject, handle, alter or log information about a request.

Examples of filters are dbfwfilter that is a configurable firewall, cache that provides query caching according to rules, regexfilter that can rewrite requests according to regular expressions, and qlafilter that logs information about requests.

Filters have sections of their own in the MaxScale configuration file that are referred to from services.


A router module is capable of routing requests to backend servers according to the characteristics of a request and/or the algorithm the router implements. Examples of routers are readconnroute that provides connection routing, that is, the server is chosen according to specified rules when the session is created and all requests are subsequently routed to that server, and readwritesplit that provides statement routing, that is, each individual request is routed to the most appropriate server.

Routers do not have sections of their own in the MaxScale configuration file, but are referred to from services.


A service abstracts a set of databases and makes them appear as a single one to the client. Depending on what router (e.g. readconnroute or readwritesplit) the service uses, the servers are used in some particular way. If the service uses filters, then all requests will be pre-processed in some way before they reach the router.

Services have sections of their own in the MaxScale configuration file.


A listener defines a port MaxScale listens on. Connection requests arriving on that port will be forwarded to the service the listener is associated with. A listener may be associated with a single service, but several listeners may be associated with the same service.

Listeners have sections of their own in the MaxScale configuration file.


The administation of MaxScale can be divided in two parts:

  • Writing the MaxScale configuration file, which is described in the following section.
  • Performing runtime modifications using MaxCtrl or MaxAdmin.

For detailed information about MaxAdmin and MaxCtrl please refer to the specific documentation referred to above. In the following it will only be explained how MaxAdmin and MaxCtrl relate to each other, as far as user credentials go.

MaxAdmin can connect to MaxScale either using Unix (domain) sockets or TCP/IP sockets. In the former case, the user is identified using her Linux credentials and by default root can access.

MaxCtrl can only connect using TCP/IP sockets. When connecting with MaxCtrl or with MaxAdmin using TCP/IP sockets, the user and password must be provided and are checked against a separate user credentials database. By default, that database contains the user admin whose password is mariadb.

Note that the database is shared between MaxAdmin and MaxCtrl, that is, if a user is deleted via MaxAdmin, then it will also no longer be possible to use that user with MaxCtrl. Similarly, a user created using MaxAdmin or MaxCtrl can be used with either MaxAdmin or MaxCtrl.

Note that if MaxAdmin (when used over a TCP/IP socket) or MaxCtrl are invoked without explicitly providing a user and password then they will by default use admin and mariadb. That means that when the default user is removed, the credentials must always be provided.

Static Configuration Parameters

The following list of global configuration parameters can NOT be changed at runtime and can only be defined in a configuration file:

  • threads
  • thread_stack_size
  • log_to_shm
  • log_augmentation
  • logdir
  • datadir
  • libdir
  • cachedir
  • piddir
  • execdir
  • connector_plugindir
  • persistdir
  • module_configdir
  • language
  • query_classifier
  • query_classifier_args
  • substitute_variables
  • sql_mode
  • local_address
  • users_refresh_time
  • load_persisted_configs
  • admin_ssl_key
  • admin_ssl_cert
  • admin_ssl_ca_cert
  • admin_enabled

All other parameters that relate to objects can be altered at runtime or can be changed by destroying and recreating the object in question.


The MariaDB MaxScale configuration is read from a file that MariaDB MaxScale will look for in the following places:

  1. By default, the file maxscale.cnf in the directory /etc
  2. The location given with the --configdir=<path> command line argument.

MariaDB MaxScale will further look for a directory with the same name as the configuration file, followed by .d (for instance /etc/maxscale.cnf.d) and recursively read all files, having a .cnf suffix, it finds in the directory hierarchy. All other files will be ignored.

There are no restrictions on how different configuration sections are arranged, but the strong suggestion is to place global settings into the configuration file MariaDB MaxScale is invoked with, and then, if deemed necessary, create separate configuration files for servers, filters, etc.

The configuration file itself is based on the .ini file format and consists of various sections that are used to build the configuration; these sections define services, servers, listeners, monitors and global settings. Parameters, which expect a comma-separated list of values can be defined on multiple lines. The following is an example of a multi-line definition.


The values of the parameter that are not on the first line need to have at least one whitespace character before them in order for them to be recognized as a part of the multi-line parameter.

Comments are defined by prefixing a row with a hash (#). Trailing comments are not supported.

# This is a comment before a parameter


Section names may not contain whitespace and must not start with the characters @@, but otherwise there are no restrictions.

Special Parameter Types


Where specifically noted, a number denoting a size can be suffixed by a subset of the IEC binary prefixes or the SI prefixes. In the former case the number will be interpreted as a certain multiple of 1024 and in the latter case as a certain multiple of 1000. The supported IEC binary suffixes are Ki, Mi, Gi and Ti and the supported SI suffixes are k, M, G and T. In both cases, the matching is case insensitive.

For instance, the following entries


are equivalent, as are the following



A number denoting a duration can be suffixed by one of the case-insensitive suffixes h, m, s and ms, for specifying durations in hours, minutes, seconds and milliseconds, respectively.

For instance, the following entries


are equivalent.

Note that if an explicit unit is not specified, then it is specific to the configuration parameter whether the duration is interpreted as seconds or milliseconds.

Not providing an explicit unit has been deprecated in MaxScale 2.4.

Regular Expressions

Many modules have settings which accept a regular expression. In most cases, these settings are named either match or exclude, and are used to filter users or queries. MaxScale uses the PCRE2-library for matching regular expressions.

When writing a regular expression (regex) type parameter to a MaxScale configuration file, the pattern string should be enclosed in slashes e.g. ^select -> match=/^select/. This clarifies where the pattern begins and ends, even if it includes whitespace. Without slashes the configuration loader trims the pattern from the ends. The slashes are removed before compiling the pattern. For backwards compatibility, the slashes are not yet mandatory. Omitting them is, however, deprecated and will be rejected in a future release of MaxScale. Currently, binlogfilter, ccrfilter, qlafilter, tee and avrorouter accept parameters in this type of regular expression form. Some other modules may not handle the slashes yet correctly.

PCRE2 supports a complicated regular expression syntax. MaxScale typically uses regular expressions simply, only checking whether the pattern and subject match at some point. For example, using the QLAFilter and setting match=/SELECT/ causes the filter to accept any query with the text "SELECT" somewhere within. To force the pattern to only match at the beginning of the query, set match=/^SELECT/. To only match the end, set match=/SELECT$/.

Modules which accept regular expression parameters also often accept options which affect how the patterns are compiled. Typically, this setting is called options and accepts values such as ignorecase, case and extended. ignorecase causes the regular expression matcher to ignore letter case, and is often on by default. extended ignores whitespace in the pattern. case turns on case-sensitive matching. These settings can also be defined in the pattern itself, so they can be used even in modules without pattern compilation settings. The pattern settings are (?i) for ignorecase and (?x) for extended. See the PCRE2 syntax documentation for more information.

Standard regular expression settings for filters

Many filters use the settings match, exclude and options. Since these settings are used in a similar way across these filters, the settings are explained here. The documentation of the filters link here and describe any exceptions to this generalized explanation.

These settings typically limit the queries the filter module acts on. match and exclude define PCRE2 regular expression patterns while options affects how both of the patterns are compiled. options works as explained above, accepting the values ignorecase, case and extended, with ignorecase being the default.

The queries are matched as they arrive to the filter on their way to a routing module. If match is defined, the filter only acts on queries matching that pattern. If match is not defined, all queries are considered to match.

If exclude is defined, the filter only acts on queries not matching that pattern. If exclude is not defined, nothing is excluded.

If both are defined, the query needs to match match but not match exclude.

Even if a filter does not act on a query, the query is not lost. The query is simply passed on to the next module in the processing chain as if the filter was not there.

Global Settings

The global settings, in a section named [MaxScale], allow various parameters that affect MariaDB MaxScale as a whole to be tuned. This section must be defined in the root configuration file which by default is /etc/maxscale.cnf.


This parameter controls the number of worker threads that are handling the events coming from the kernel. The default is 1 thread. It is recommended that you start with one thread and increase the number if you require greater performance. Increasing the amount of worker threads beyond the number of processor cores does not improve the performance, rather is likely to degrade it, and can consume resources needlessly.

You can enable automatic configuration of this value by setting the value to auto. This way MariaDB MaxScale will detect the number of available processors and set the amount of threads to be equal to that number. This should only be used for systems dedicated for running MariaDB MaxScale.

# Valid options are:
#       threads=[<number of threads> | auto ]


Additional threads will be created to execute other internal services within MariaDB MaxScale. This setting is used to configure the number of threads that will be used to manage the user connections.


Ignored and deprecated in 2.3.

If you need to explicitly set the stack size, do so using ulimit -s before starting MaxScale.


The connection timeout in seconds for the MySQL connections to the backend server when user authentication data is fetched. Increasing the value of this parameter will cause MariaDB MaxScale to wait longer for a response from the backend server before aborting the authentication process. The default is 3 seconds.


The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.


The read timeout in seconds for the MySQL connection to the backend database when user authentication data is fetched. Increasing the value of this parameter will cause MariaDB MaxScale to wait longer for a response from the backend server when user data is being actively fetched. If the authentication is failing and you either have a large number of database users and grants or the connection to the backend servers is slow, it is a good idea to increase this value. The default is 1 second.


The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.


The write timeout in seconds for the MySQL connection to the backend database when user authentication data is fetched. Currently MariaDB MaxScale does not write or modify the data in the backend server. The default is 2 seconds.


The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.


The number of times an interrupted internal query will be retried. The default is to retry the query once. This feature was added in MaxScale 2.1.10 and was disabled by default until MaxScale 2.3.0.

An interrupted query is any query that is interrupted by a network error. Connection timeouts are included in network errors and thus is it advisable to make sure that the value of query_retry_timeout is set to an adequate value. Internal queries are only used to retrieve authentication data and monitor the servers.


The total timeout in seconds for any retried queries. The default value is 5 seconds.

An interrupted query is retried for either the configured amount of attempts or until the configured timeout is reached.

The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.


Controls whether MaxScale is a passive node in a cluster of multiple MaxScale instances. The default value is false.

This parameter is intended to be used with multiple MaxScale instances that use failover functionality to manipulate the cluster in some form. Passive nodes only observe the clusters being monitored and take no direct actions.

The following functionality is disabled when passive mode is enabled:

  • Automatic failover in the mariadbmon module
  • Automatic rejoin in the mariadbmon module
  • Launching of monitor scripts

NOTE: Even if MaxScale is in passive mode, it will still accept clients and route any traffic sent to it. The only operations affected by the passive mode are the ones listed above.


Enable or disable the high precision timestamps in logfiles. Enabling this adds millisecond precision to all logfile timestamps.

# Valid options are:
#       ms_timestamp=<0|1>


Skip service and monitor user permission checks. This is useful when you know the permissions are OK and you want to speed up the startup process. This parameter takes a boolean value and is disabled by default.

It is recommended to not disable the permission checks so that any missing privileges are detected when maxscale is starting up. If you are experiencing a slow startup of MaxScale due to large amounts of connection timeouts when permissions are checked, disabling the permission checks could speed up the startup process.



Enable or disable the logging of messages to syslog.

By default logging to syslog is enabled.

# Valid options are:
#       syslog=<0|1>

To enable logging to syslog use the value 1 and to disable use the value 0.


Enable to disable to logging of messages to MariaDB MaxScale's log file.

By default logging to maxlog is enabled.

# Valid options are:
#       syslog=<0|1>

To enable logging to the MariaDB MaxScale log file use the value 1 and to disable use the value 0.


Note: This parameter has been removed in 2.4.0: do not use it

In older MaxScale versions, the actual log file was created in /dev/shm and a symbolic link to that file was stored in place of the normal MaxScale log. If you want to store the log in shared memory, define the directory with logdir in /dev/shm.


Enable or disable the logging of messages whose syslog priority is warning. Messages of this priority are enabled by default.

# Valid options are:
#       log_warning=<0|1>

To disable these messages use the value 0 and to enable them use the value 1.


Enable or disable the logging of messages whose syslog priority is notice. Messages of this priority provide information about the functioning of MariaDB MaxScale and are enabled by default.

# Valid options are:
#       log_notice=<0|1>

To disable these messages use the value 0 and to enable them use the value 1.


Enable or disable the logging of messages whose syslog priority is info. These messages provide detailed information about the internal workings of MariaDB MaxScale and should not, due to their frequency, be enabled, unless there is a specific reason for that. For instance, from these messages it will be evident, e.g., why a particular query was routed to the master instead of to a slave. These informational messages are disabled by default.

# Valid options are:
#       log_info=<0|1>

To disable these messages use the value 0 and to enable them use the value 1.


Enable or disable the logging of messages whose syslog priority is debug. This kind of messages are intended for development purposes and are disabled by default. Note that if MariaDB MaxScale has been built in release mode, then debug messages are excluded from the build and this setting will not have any effect.

# Valid options are:
#       log_debug=<0|1>

To disable these messages use the value 0 and to enable them use the value 1.


Deprecated Use log_notice instead.


Deprecated Use log_info instead.


Enable or disable the augmentation of messages. If this is enabled, then each logged message is appended with the name of the function where the message was logged. This is primarily for development purposes and hence is disabled by default.

# Valid options are:
#       log_augmentation=<0|1>

To disable the augmentation use the value 0 and to enable it use the value 1.


It is possible that a particular error (or warning) is logged over and over again, if the cause for the error persistently remains. To prevent the log from flooding, it is possible to specify how many times a particular error may be logged within a time period, before the logging of that error is suppressed for a while.

# A valid value looks like
#       log_throttling = X, Y, Z
# where the first value X is a positive integer and means the number of times
# a specific error may be logged within a duration of Y, before the logging
# of that error is suppressed for a duration of Z.
log_throttling=8, 2s, 15000ms

In the example above, the logging of a particular error will be suppressed for 15 seconds if the error has been logged 8 times in 2 seconds.

The default is 10, 1000ms, 10000ms, which means that if the same error is logged 10 times in one second, the logging of that error is suppressed for the following 10 seconds.

To disable log throttling, add an entry with an empty value


or one where any of the integers is 0.

log_throttling=0, 0, 0

The durations can be specified as documented here. If no explicit unit is provided, the value is interpreted as milliseconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected.

Note that notice, info and debug messages are never throttled.


Set the directory where the logfiles are stored. The folder needs to be both readable and writable by the user running MariaDB MaxScale.



Set the directory where the data files used by MariaDB MaxScale are stored. Modules can write to this directory and for example the binlogrouter uses this folder as the default location for storing binary logs.

This is also the directory where the password encryption key is read from that is generated by maxkeys.



Set the directory where MariaDB MaxScale looks for modules. The library directory is the only directory that MariaDB MaxScale uses when it searches for modules. If you have custom modules for MariaDB MaxScale, make sure you have them in this folder.



Configure the directory MariaDB MaxScale uses to store cached data. An example of cached data is the authentication data fetched from the backend servers. MariaDB MaxScale stores this in case a connection to the backend server is not possible.



Configure the directory for the PID file for MariaDB MaxScale. This file contains the Process ID for the running MariaDB MaxScale process.



Configure the directory where the executable files reside. All internal processes which are launched will use this directory to look for executable files.



Location of the MariaDB Connector-C plugin directory. The MariaDB Connector-C used in MaxScale can use this directory to load authentication plugins. The versions of the plugins must be binary compatible with the connector version that MaxScale was built with.



Configure the directory where persisted configurations are stored. When a new server is created via MaxAdmin, it will be stored in this directory. Do not use or modify the contents of this directory, use /etc/maxscale.cnf.d/ instead.



Configure the directory where module configurations are stored. Path arguments are resolved relative to this directory. This directory should be used to store module specific configurations e.g. dbfwfilter rule files.

Any configuration parameter that is not an absolute path will be interpreted as a relative path. The relative paths use the module configuration directory as the working directory.

For example, the configuration parameter file=my_file.txt would be interpreted as /etc/maxscale.cnf.d/my_file.txt whereas file=/home/user/my_file.txt would be interpreted as /home/user/my_file.txt.



Set the folder where the errmsg.sys file is located in. MariaDB MaxScale will look for the errmsg.sys file installed with MariaDB MaxScale from this folder.



The module used by MariaDB MaxScale for query classification. The information provided by this module is used by MariaDB MaxScale when deciding where a particular statement should be sent. The default query classifier is qc_sqlite.


Specifies the maximum size of the query classifier cache. The default limit is 15% of total system memory starting with MaxScale 2.3.7. In older versions the default limit was 40% of total system memory. This feature was added in MaxScale 2.3.0.

When the query classifier cache has been enabled, MaxScale will, after a statement has been parsed, store the classification result using the canonicalized version of the statement as the key.

If the classification result for a statement is needed, MaxScale will first canonicalize the statement and check whether the result can be found in the cache. If it can, the statement will not be parsed at all but the cached result is used.

The configuration parameter takes one integer that specifies the maximum size of the cache. The size of the cache can be specifed as explained here.

# 1MB query classifier cache

Note that MaxScale uses a separate cache for each worker thread. To obtain the amount of memory available for each thread, divide the cache size with the value of threads. If statements are evicted from the cache (visible in the diagnostic output), consider increasing the cache size.

Using maxctrl show threads it is possible to check what the actual size of the cache is and to see performance statistics.

Key Meaning
QC cache size The current size of the cache (bytes).
QC cache inserts How many entries have been inserted into the cache.
QC cache hits How many times the classification result has been found from the cache.
QC cache misses How many times the classification result has not been found from the cache, but the classification had to be performed.
QC cache evictions How many times a cache entry has had to be removed from the cache, in order to make place for another.


Arguments for the query classifier. What arguments are accepted depends on the particular query classifier being used. The default query classifier - qc_sqlite - supports the following arguments:


An integer argument taking the following values: * 0: Nothing is logged. This is the default. * 1: Statements that cannot be parsed completely are logged. They may have been partially parsed, or classified based on keyword matching. * 2: Statements that cannot even be partially parsed are logged. They may have been classified based on keyword matching. * 3: Statements that cannot even be classified by keyword matching are logged.


This will log all statements that cannot be parsed completely. This may be useful if you suspect that MariaDB MaxScale routes statements to the wrong server (e.g. to a slave instead of to a master).


Enable or disable the substitution of environment variables in the MaxScale configuration file. If the substitution of variables is enabled and a configuration line like


is encountered, then $SOME_VALUE will be replaced with the actual value of the environment variable SOME_VALUE. Note: Variable substitution will be made only if '$' is the first character of the value. Everything following '$' is interpreted as the name of the environment variable. * Referring to a non-existing environment variable is a fatal error.

By default, the value of substitute_variables is false.


The setting of substitute_variables will have an effect on all parameters in the all other sections, irrespective of where the [maxscale] section is placed in the configuration file. However, in the [maxscale] section, to ensure that substitution will take place, place the substitute_variables=true line first.


Specifies whether the query classifier parser should initially expect MariaDB or PL/SQL kind of SQL.

The allowed values are: default: The parser expects regular MariaDB SQL. oracle : The parser expects PL/SQL.


The default value is default.

NOTE If sql_mode is set to oracle, then MaxScale will also assume that autocommit initially is off.

At runtime, MariaDB MaxScale will recognize statements like

set sql_mode=oracle;


set sql_mode=default;

and change mode accordingly.

NOTE If set sql_mode=oracle; is encountered, then MaxScale will also behave as if autocommit had been turned off and conversely, if set sql_mode=default; is encountered, then MaxScale will also behave as if autocommit had been turned on.

Note that MariaDB MaxScale is not explicitly aware of the sql mode of the server, so the value of sql_mode should reflect the sql mode used when the server is started.


What specific local address/interface to use when connecting to servers.

This can be used for ensuring that MaxScale uses a particular interface when connecting to servers, in case the computer MaxScale is running on has multiple interfaces.



How often, in seconds, MaxScale at most may refresh the users from the backend server.

MaxScale will at startup load the users from the backend server, but if the authentication of a user fails, MaxScale assumes it is because a new user has been created and will thus refresh the users. By default, MaxScale will do that at most once per 30 seconds and with this configuration option that can be changed. A value of 0 allows infinite refreshes and a negative value disables the refreshing entirelly. Note that using maxadmin it is possible to explicitly cause the users of a service to be reloaded.


The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.

In MaxScale 2.3.9 and older versions, the minimum allowed value was 10 seconds but, due to a bug, the default value was 0 which allowed infinite refreshes.


How many statements MaxScale should store for each session. This is for debugging purposes, as in case of problems it is often of value to be able to find out exactly what statements were sent before a particular problem turned up.

Note: See also dump_last_statements using which the actual dumping of the statements is enabled. Unless both of the parameters are defined, the statement dumping mechanism doesn't work.


Default is 0.


With this configuration item it is specified in what circumstances MaxScale should dump the last statements that a client sent. The allowed values are never, on_error and on_close. With never the statements are never logged, with on_error they are logged if the client closes the connection improperly, and with on_close they are always logged when a client session is closed.


Default is never.

Note that you need to specify with retain_last_statements how many statements MaxScale should retain for each session. Unless it has been set to another value than 0, this configuration setting will not have an effect.


How many log entries are stored in the session specific trace log. This log is written to disk when a session ends abnormally and can be used for debugging purposes. It would be good to enable this if a session is disconnected and the log is not detailed enough. In this case the info log might reveal the true cause of why the connection was closed.


Default is 0.

The session trace log is also exposed by REST API and is shown with maxctrl show sessions.


High water mark for network write buffer. Controls when network traffic throtting is started. The parameter accepts size type values.

More specifically, if the client side write queue is above this value, it will block traffic coming from backend servers. If the backend side write queue is above this value, it will block traffic from client. the minimum allowed size is 4096 bytes.

Only when both writeq_high_water and writeq_low_water are set, traffic throtting is enabled. By default, traffic throttling is disabled.


Low water mark for network write buffer. Once the traffic throttling is enabled, it will only be disabled when the write queue is below writeq_low_water. The parameter accepts size type values. The minimum allowed size is 512 bytes. writeq_high_water must always be greater than writeq_low_water.


Load persisted runtime changes on startup. This parameter accepts boolean values and is enabled by default. This parameter was added in MaxScale 2.3.6.

All runtime configuration changes are persisted in generated configuration files located by default in /var/lib/maxscale/maxscale.cnf.d/ and are loaded on startup after main configuration files have been read. To make runtime configurations volatile (i.e. they are lost when maxscale is restarted), use load_persisted_configs=false. All changes are still persisted since it stores the current runtime state of MaxScale. This makes problem analysis easier if an unexpected outage happens.


The maximum number of authentication failures that are tolerated before a host is temporarily blocked. The default value is 10 failures. After a host is blocked, connections from it are rejected for 60 seconds. To disable this feature, set the value to 0.

Note that the configured value is not a hard limit. The number of tolerated failures is between max_auth_errors_until_block and threads * max_auth_errors_until_block where max_auth_errors_until_block is the configured value of this parameter and threads is the number of configured threads.

REST API Configuration

The MaxScale REST API is an HTTP interface that provides JSON format data intended to be consumed by monitoring appllications and visualization tools.

The following options must be defined under the [maxscale] section in the configuration file.


The network interface where the REST API listens on. The default value is the IPv4 address which only listens for local connections.


The port where the REST API listens on. The default value is port 8989.


Enable REST API authentication using HTTP Basic Access authentication. This is not a secure method of authentication without HTTPS but it does add a small layer of security. This option is enabled by default.

The admin interface authentication uses the same user as MaxAdmin network interface. This means that new users can be added with both MaxAdmin and the REST API. The default credentials for the interface are admin:mariadb.


The path to the TLS private key in PEM format for the admin interface.

If the admin_ssl_key and admin_ssl_cert options are all defined, the admin interface will use encrypted HTTPS instead of plain HTTP.


The path to the TLS public certificate in PEM format. See admin_ssl_key documentation for more details.


The path to the TLS CA certificate in PEM format. If defined, the client certificate, if provided, will be validated against it. This parameter is optional starting with MaxScale 2.3.19.


Enable or disable the admin interface. This allows the admin interface to be completely disabled to prevent access to it.


Log authentication failures for the admin interface. This parameter expects a boolean value and is enabled by default.

admin_pam_readwrite_service and admin_pam_readonly_service

Use Pluggable Authentication Modules (PAM) for REST API authentication. The settings accept a PAM service name which is used during authentication if normal authentication fails. admin_pam_readwrite_service should accept users who can do any MaxCtrl/REST-API-operation. admin_pam_readonly_service should accept users who can only do read operations. Because REST-API does not support back and forth communication between the client and MaxScale, the PAM services must be simple. They should only ask for the password and nothing else.

If only admin_pam_readwrite_service is configured, both read and write operations can be authenticated by PAM. If only admin_pam_readonly_service is configured, only read operations can be authenticated by PAM. If both are set, the service used is determined by the requested operation. Leave or set both empty to disable PAM for REST-API.


MaxScale logs warnings and errors for various reasons and often it is self- evident and generally applicable whether some occurence should warrant a warning or an error, or perhaps just an info-level message.

However, there are events whose seriousness is not self-evident. For instance, in some environments an authentication failure may simply indicate that someone has made a typo, while in some other environment that can only happen in case there has been a security breech.

To handle events like these, MaxScale defines events whose logging facility and level can be controlled by the administrator. Given an event X, its facility and level are controlled in the following manner:


The above means that if event X occurs, then that is logged using the facility LOG_LOCAL0 and the level LOG_ERR.

The valid values of facilityare the facility values reported byman syslog, e.g.LOG_AUTH,LOG_LOCAL0andLOG_USER. Likewise, the valid values forlevelare the ones also reported byman syslog, e.g.LOG_WARNING,LOG_ERRandLOG_CRIT`.

Note that MaxScale does not act upon the level, that is, even if the level of a particular event is defined to be LOG_EMERG, MaxScale will not shut down if that event occurs.

The default facility is LOG_USER and the default level is LOG_WARNING.

The available events are:


This event occurs when there is an authentication failure.



A service represents the database service that MariaDB MaxScale offers to the clients. In general a service consists of a set of backend database servers and a routing algorithm that determines how MariaDB MaxScale decides to send statements or route connections to those backend servers.

A service may be considered as a virtual database server that MariaDB MaxScale makes available to its clients.

Several different services may be defined using the same set of backend servers. For example a connection based routing service might be used by clients that already performed internal read/write splitting, whilst a different statement based router may be used by clients that are not written with this functionality in place. Both sets of applications could access the same data in the same databases.

A service is identified by a service name, which is the name of the configuration file section and a type parameter of service.


In order for MariaDB MaxScale to forward any requests it must have at least one service defined within the configuration file. The definition of a service alone is not enough to allow MariaDB MaxScale to forward requests however, the service is merely present to link together the other configuration elements.


The router parameter of a service defines the name of the router module that will be used to implement the routing algorithm between the client of MariaDB MaxScale and the backend databases. Additionally routers may also be passed a comma separated list of options that are used to control the behavior of the routing algorithm. The two parameters that control the routing choice are router and router_options. The router options are specific to a particular router and are used to modify the behavior of the router. The read connection router can be passed options of master, slave or synced, an example of configuring a service to use this router and limiting the choice of servers to those in slave state would be as follows.


To change the router to connect on to servers in the master state as well as slave servers, the router options can be modified to include the master state.


A more complete description of router options and what is available for a given router is included with the documentation of the router itself.


Option string given to the router module. The value of this parameter should be a comma-separated list of key-value pairs. See router specific documentation for more details.


The filters option allow a set of filters to be defined for a service; requests from the client are passed through these filters before being sent to the router for dispatch to the backend server. The filters parameter takes one or more filter names, as defined within the filter definition section of the configuration file. Multiple filters are separated using the | character.

filters=counter | QLA

The requests pass through the filters from left to right in the order defined in the configuration parameter.


The servers parameter in a service definition provides a comma separated list of the backend servers that comprise the service. The server names are those used in the name section of a block with a type parameter of server (see below).


NOTE The servers parameter is mutually exclusive with the cluster parameter.


The servers the service uses are defined by the monitor specified as value of this configuration parameter.


NOTE The clusters parameter is mutually exclusive with the servers parameter.


The user parameter, along with the password parameter are used to define the credentials used to connect to the backend servers to extract the list of database users from the backend database that is used for the client authentication.


Authentication of incoming connections is performed by MariaDB MaxScale itself rather than by the database server to which the client is connected. The client will authenticate itself with MariaDB MaxScale, using the username, hostname and password information that MariaDB MaxScale has extracted from the backend database servers. For a detailed discussion of how this impacts the authentication process please see the "Authentication" section below.

The host matching criteria is restricted to IPv4, IPv6 will be added in a future release.

Existing user configuration in the backend databases must be checked and may be updated before successful MariaDB MaxScale authentication:

In order for MariaDB MaxScale to obtain all the data it must be given a username it can use to connect to the database and retrieve that data. This is the parameter that gives MariaDB MaxScale the username to use for this purpose.

The account used must be able to select from the mysql.user table, the following is an example showing how to create this user.

CREATE USER 'maxscale'@'maxscalehost' IDENTIFIED BY 'maxscale-password';

Additionally, SELECT privileges on the mysql.user, mysql.db and mysql.tables_priv tables and SHOW DATABASES privileges are required in order to load databases name and grants suitable for database name authorization.

GRANT SELECT ON mysql.user TO 'maxscale'@'maxscalehost';
GRANT SELECT ON mysql.db TO 'maxscale'@'maxscalehost';
GRANT SELECT ON mysql.tables_priv TO 'maxscale'@'maxscalehost';
GRANT SELECT ON mysql.roles_mapping TO 'maxscale'@'maxscalehost';
GRANT SHOW DATABASES ON *.* TO 'maxscale'@'maxscalehost';

-- MariaDB from 10.2.2 to 10.2.10 requires extra grants
GRANT SELECT ON mysql.* TO 'maxscale'@'maxscalehost';

Note: MariaDB versions 10.2.10 and older require a SELECT grant on mysql.* in addition to the normal grants. This is to work around MDEV-13453 which was fixed in MariaDB 10.2.11.

If you are using MariaDB ColumnStore, the follwing grant is requried.

GRANT ALL ON infinidb_vtable.* TO 'maxscale'@'maxscalehost';

See MaxScale Troubleshooting for more information on how to troubleshoot authentication related problems.


The password parameter provides the password information for the above user and may be either a plain text password or it may be an encrypted password. See the section on encrypting passwords for use in the maxscale.cnf file. This user must be capable of connecting to the backend database and executing these SQL statements to load database names and grants from the backends:

  • SELECT user, host, password,Select_priv FROM mysql.user.
  • SELECT user, host, db FROM mysql.db

Note: In older versions of MaxScale this parameter was called passwd. The use of passwd was deprecated in MaxScale 2.3.0.


This parameter controls the ability of the root user to connect to MariaDB MaxScale and hence onwards to the backend servers via MariaDB MaxScale.

The default value is 0, disabling the ability of the root user to connect to MariaDB MaxScale.

Example for enabling root user:


Values of on or true may also be given to enable the root user and off or false may be given to disable the use of the root user.



This parameter enables matching of local addresses (i.e. against the wildcard host, %, for authentication. This parameter is enabled by default.

If this parameter is disabled, in order to authenticate a connection from the same machine as the one on which MariaDB MaxScale is running, an explicit user@localhost entry will be required in the MySQL user table.


This parameter sets a custom version string that is sent in the MySQL Handshake from MariaDB MaxScale to clients.



If not set, the default value is 5.5.5-10.0.0 MaxScale <MaxScale version> where <MaxScale version> is the version of MaxScale. If the provided string does not start with the number 5, a 5.5.5- prefix will be added to it. This means that a version_string value of MaxScale-Service would result in a 5.5.5-MaxScale-Service being sent to the client.


Note: This parameter has been deprecated in MaxScale 2.3.2. A rank mechanism will be added in MaxScale 2.4 to allow better control over server usage.

The weightby parameter is used in conjunction with server parameters in order to control the load balancing applied in the router in use by the service. This allows varying weights to be applied to each server to create a non-uniform distribution of the load amongst the servers.

An example of this might be to define a parameter for each server that represents the amount of resource available on the server, we could call this serversize. Every server should then have a serversize parameter set for the server.


The service would then have the parameter weightby=serv_weight. If there are 4 servers defined in the service (serverA, serverB, serverC and serverD) with the serversize set as shown in the table below, the connections would balanced using the percentages in this table.

Server serversize % connections
serverA 10 18%
serverB 15 27%
serverC 10 18%
serverD 20 36%

Note: If the value of the weighting parameter of an individual server is zero or the relative weight rounds down to zero, no queries will be routed to that server as long as a server with a positive weight is available.

Here is an excerpt from an example configuration with the serv_weight parameter used as the weighting parameter.




With this configuration and a heavy query load, the server server1 will get most of the connections and about a third of the remaining queries are routed to the second server. With server weights, you can assign secondary servers that are only used when the primary server is under heavy load.

Without the weightby parameter, each connection counts as a single connection. With a weighting parameter, a single connection received its weight from the server's own weighting parameter divided by the sum of all weighting parameters in all the configured servers.

If we use the previous configuration as an example, the sum of the serv_weight parameter is 4. Server1 would receive a weight of 3/4=75% and server2 would get 1/4=25%. This means that server1 would get 75% of the connections and server2 would get 25% of the connections.


This parameter controls whether only a single server or all of the servers are used when loading the users from the backend servers. This takes a boolean value and when enabled, creates a union of all the users and grants on all the servers.


The strip_db_esc parameter strips escape characters from database names of grants when loading the users from the backend server.

This parameter takes a boolean value and when enabled, will strip all backslash (\) characters from the database names. The default value for this parameter is true since MaxScale 2.0.1. In previous version, the default value was false.

Some visual database management tools automatically escape some characters and this might cause conflicts when MariaDB MaxScale tries to authenticate users.


Note: This feature is ignored by MaxScale 2.4 and will be removed in future versions. This is due to the fact that a failure to bind to a network interface is a serious error which should always be investigated and is not related to network outages.

The retry_on_failure parameter controls whether MariaDB MaxScale will try to restart failed services and accepts a boolean value. This functionality is enabled by default to prevent services being permanently disabled if the starting of the service failed due to a network outage. Disabling the restarting of the failed services will cause them to be permanently disabled if the services can't be started when MariaDB MaxScale is started.


Enable or disable the logging of authentication failures and warnings. This parameter takes a boolean value.

MariaDB MaxScale normally suppresses warning messages about failed authentication. Enabling this option will log those messages into the message log with details about who tried to connect to MariaDB MaxScale and from where.


The connection_timeout parameter is used to disconnect sessions to MariaDB MaxScale that have been idle for too long. The session timeouts are disabled by default. To enable them, define the timeout in seconds in the service's configuration section. A value of zero is interpreted as no timeout, the same as if the parameter is not defined.

The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.

Warning: If a connection is idle for longer than the configured connection timeout, it will be forcefully disconnected and a warning will be logged in the MaxScale log file. If you are performing long-running maintenance operations (e.g. ALTER TABLE) either do them with a direct connection to the server or set connection_timeout to zero before executing them.




The maximum number of simultaneous connections MaxScale should permit to this service. If the parameter is zero or is omitted, there is no limit. Any attempt to make more connections after the limit is reached will result in a "Too many connections" error being returned.




Note: This feature has been removed from MaxScale 2.4. See retry_on_failure for more details.

Configure the maximum interval between consecutive attempts to bind to an interface. The default value for this parameter is 3600 seconds. This parameter was introduced in MaxScale 2.2.0.

When a listener fails to bind to the interface it is assigned to, it will attempt to bind to the interface again after 10 seconds. If the attempt fails, the interval is incremented by 10 seconds and the next attempt will be in 20 seconds. The interval is incremented until the value of max_retry_interval is reached at which point the listener attempts to bind to the interface every max_retry_interval seconds.

The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the interval is seconds, an interval specified in milliseconds will be rejected, even if the duration is longer than a second.


Enable or disable session transaction state tracking by offloading it to the backend servers. Getting current session transaction state from server side will be more accurate for that state inside stored procedures or prepare statments will be handle properly, and that is also faster as no parsing is needed on MaxScale.

This is only supported by MariaDB versions 10.3 or newer. Default is false. The following Server side config is needed too.

session_track_state_change = ON
session_track_transaction_info = CHARACTERISTICS


How many statements MaxScale should store for each session of this service. This overrides the value of the global setting with the same name. If retain_last_statements has been specified in the global section of the MaxScale configuration file, then if it has not been explicitly specified for the service, the global value holds, otherwise the service specific value rules. That is, it is possible to enable the setting globally and turn it off for a specific service, or just enable it for specific services.

The value of this parameter can be changed at runtime using maxctrl and the new value will take effect for sessions created thereafter.

maxctrl alter service MyService retain_last_statements 5


This parameter controls how long a network write to the client can stay buffered. This feature is disabled by default.

When net_write_timeout is configured and data is buffered on the client network connection, if the time since the last successful network write exceeds the configured limit, the client connection will be disconnected.

The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.


Server sections are used to define the backend database servers that can be formed into a service. A server may be a member of one or more services within MariaDB MaxScale. Servers are identified by a server name which is the section name in the configuration file. Servers have a type parameter of server, plus address port and protocol parameters.



The IP address or hostname of the machine running the database server that is being defined. MariaDB MaxScale will use this address to connect to the backend database server.


The port on which the database listens for incoming connections. MariaDB MaxScale will use this port to connect to the database server. The default value is 3306.


The absolute path to a UNIX domain socket the MariaDB server is listening on. Either address or socket must be defined and defining them both is an error.


The name for the protocol module to use to connect MariaDB MaxScale to the database. Currently only one backend protocol is supported, the MariaDBBackend module.


The monitor has a username and password that is used to connect to all servers for monitoring purposes, this may be overridden by supplying a monitoruser statement for each individual server.



The monitor has a username and password that is used to connect to all servers for monitoring purposes, this may be overridden by supplying a monitorpw for the individual servers.


The monitorpw parameter may be either a plain text password or it may be an encrypted password. See the section on encrypting passwords for use in the maxscale.cnf file.


An alternative port used to monitor the server. This allows MaxScale to connect even when max_connections has been reached on the backend server. If this parameter is defined and a connection to the normal port fails, the alternative port is used.

For more information, read the extra_port documentation.


The persistpoolmax parameter defaults to zero but can be set to an integer value for a back end server. If it is non zero, then when a DCB connected to a back end server is discarded by the system, it will be held in a pool for reuse, remaining connected to the back end server. If the number of DCBs in the pool has reached the value given by persistpoolmax then any further DCB that is discarded will not be retained, but disconnected and discarded.


The persistmaxtime parameter defaults to zero but can be set to a duration as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the parameter is seconds, a value specified in milliseconds will be rejected, even if the duration is longer than a second.

A DCB placed in the persistent pool for a server will only be reused if the elapsed time since it joined the pool is less than the given value. Otherwise, the DCB will be discarded and the connection closed.

For more information about persistent connections, please read the Administration Tutorial.


If proxy_protocol is set to on, MaxScale will send a PROXY protocol header when connecting client sessions to the server. The header contains the original client IP address and port, as seen by MaxScale. The server will then read the header and perform authentication as if the connection originated from this address instead of MaxScale's IP address. With this feature, the user accounts on the backend server can be simplified to only contain the actual client hosts and not the MaxScale host.

PROXY protocol will be supported by MariaDB 10.3, which this feature has been tested with. To use it, enable the PROXY protocol in MaxScale for every compatible server and configure the MariaDB servers themselves to accept the protocol headers from MaxScale's IP address. On the server side, the protocol should be enabled only for trusted IPs, as it allows the sender to spoof the connection origin. If a proxy header is sent to a server not expecting it, the connection will fail. Usually PROXY protocol should be enabled for every server in a cluster, as they typically have similar grants.

Other SQL-servers may support PROXY protocol as well, but the implementation may be highly restricting. Strict adherence to the protocol requires that the backend server does not allow mixing of un-proxied and proxied connections from a given IP. MaxScale requires normal connections to backends for monitoring and authentication data queries, which would be blocked. To bypass this restriction, the server monitor needs to be disabled and the service listener needs to be configured to disregard authentication errors (skip_authentication=true). Server states also need to be set manually in MaxAdmin. These steps are not required for MariaDB 10.3, since its implementation is more flexible and allows both PROXY-headered and headerless connections from a proxy-enabled IP.


The authenticator module to use. Each protocol module defines a default authentication module which is used if no authenticator parameter is found from the configuration.


Removed feature. Only client authenticator modules have options, in the listener definition. Server authenticator options in the config file are ignored.


This parameter specifies how full a disk may be, before MaxScale should start logging warnings or take other actions (e.g. perform a switchover). This functionality will only work with MariaDB server versions 10.1.32, 10.2.14 and 10.3.6 onwards, if the DISKS information schema plugin has been installed.

NOTE: In future MariaDB versions, the information will be available only if the monitor user has the FILE privilege.

A limit is specified as a path followed by a colon and a percentage specifying how full the corresponding disk may be, before action is taken. E.g. an entry like


specifies that the disk that has been mounted on /data may be used until 80% of the total space has been consumed. Multiple entries can be specified by separating them by a comma. If the path is specified using *, then the limit applies to all disks. However, the value of * is only applied if there is not an exact match.

Note that if a particular disk has been mounted on several paths, only one path need to be specified. If several are specified, then the one with the smallest percentage will be applied.



The last line means that the disk mounted at /data1 may be used up to 80%, the disk mounted at /data2 may be used up to 60% and all other disks mounted at any paths may be used up until 90% of maximum capacity, before MaxScale starts to warn to take action.

Note that the path to be used, is one of the paths returned by:

> use information_schema;
> select * from disks;
| Disk      | Path                 | Total     | Used     | Available |
| /dev/sda3 | /                    |  47929956 | 34332348 |  11139820 |
| /dev/sdb1 | /data                | 961301832 |    83764 | 912363644 |

There is no default value, but this parameter must be explicitly specified if the disk space situation should be monitored.


This parameter controls the order in which servers are used. Valid values for this parameter are primary and secondary. The default value is primary. This parameter replaces the use of the weightby parameter as the primary means of controlling server usage.

This behavior depends on the router implementation but the general rule of thumb is that primary servers will be used before secondary servers.

Readconnroute will always use primary servers before secondary servers as long as they match the configured server type.

Readwritesplit will pick servers that have the same rank as the current master. Read the readwritesplit documentation on server ranks for a detailed description of the behavior.

The following example server configuration demonstrates how rank can be used to exclude DR-site servers from routing.





The main-site-master and main-site-slave servers will be used as long as they are available. When they are no longer available, the DR-site-master and DR-site-slave will be used.


Monitor sections are used to define the monitoring module that watches a set of servers. Each server can only be monitored by one monitor.

Common monitor parameters can be found here.


The listener defines a port and protocol pair that is used to listen for connections to a service. A service may have multiple listeners associated with it, either to support multiple protocols or multiple ports. As with other elements of the configuration the section name is the listener name and it can be selected freely. A type parameter is used to identify the section as a listener definition. Address is optional and it allows the user to limit connections to certain interface only. Socket is also optional and used for Unix socket connections.

The network socket where the listener listens will have a backlog of connections. The size of this backlog is controlled by the net.ipv4.tcp_max_syn_backlog and net.core.somaxconn kernel parameters.

Increasing the size of the backlog by modifying the kernel parameters helps with sudden connection spikes and rejected connections. For more information see listen(2).

[<Listener name>]
service=<Service name>]
port=<Listen port number>


The service to which the listener is associated. This is the name of a service that is defined elsewhere in the configuration file.


The name of the protocol module that is used for the communication between the client and MariaDB MaxScale itself.


The address option sets the address that will be used to bind the listening socket. The address may be specified as an IP address in 'dot notation' or as a hostname. If the address option is not included in the listener definition the listener will bind to all network interfaces.


The port to use to listen for incoming connections to MariaDB MaxScale from the clients. If the port is omitted from the configuration a default port for the protocol will be used.


The socket option may be included in a listener definition, this configures the listener to use Unix domain sockets to listen for incoming connections. The parameter value given is the name of the socket to use.

Note: If you want to use both network ports and UNIX domain sockets with a service, define two separate listeners that connect to the same service.


The authenticator module to use. Each protocol module defines a default authentication module which is used if no authenticator parameter is found from the configuration.


Option string given to the authenticator module. The value of this parameter should be a comma-separated list of key-value pairs. See authenticator specific documentation for more details.

Available Protocols

The protocols supported by MariaDB MaxScale are implemented as external modules that are loaded dynamically into the MariaDB MaxScale core. They allow MariaDB MaxScale to communicate in various protocols both on the client side and the backend side. Each of the protocols can be either a client protocol or a backend protocol. Client protocols are used for client-MariaDB MaxScale communication and backend protocols are for MariaDB MaxScale-database communication.


This is the implementation of the MySQL protocol that is used by clients of MariaDB MaxScale to connect to MariaDB MaxScale.


The MariaDBBackend protocol module is the implementation of the protocol that MariaDB MaxScale uses to connect to the backend MariaDB, MySQL and Percona Server databases. This implementation is tailored for the MariaDB MaxScale to MySQL Database traffic and is not a general purpose implementation of the MySQL protocol.


Note: This module is deprecated.

The protocol used used by the maxadmin client application in order to connect to MariaDB MaxScale and access the command line interface.


Note: This module is deprecated: use the REST API instead.

This protocol module is currently still under development, it provides a means to create HTTP connections to MariaDB MaxScale for use by web browsers or RESTful API clients.

TLS/SSL encryption

This section describes configuration parameters for both servers and listeners that control the TLS/SSL encryption method and the various certificate files involved in it.

To enable TLS/SSL for a listener, you must set the ssl parameter to true and provide at least the ssl_cert and ssl_key parameters.

To enable TLS/SSL for a server, you must set the ssl parameter to true. If the backend database server has certificate verification enabled, the ssl_cert and ssl_key parameters must also be defined.

Custom CA certificates can be defined with the ssl_ca_cert parameter.

After this, MaxScale connections between the server and/or the client will be encrypted. Note that the database must also be configured to use TLS/SSL connections if backend connection encryption is used.

Note: MaxScale does not allow mixed use of TLS/SSL and normal connections on the same port.

If TLS encryption is enabled for a listener, any unencrypted connections to it will be rejected. MaxScale does this to improve security by preventing accidental creation of unencrypted connections.

The separation of secure and insecure connections differs from the MariaDB server which allows both secure and insecure connections on the same port. As MaxScale is the gateway through which all connections go, in order to guarantee a more secure system MaxScale enforces a stricter security policy than what the server does.


This enables SSL connections when set to true. The parameter takes a boolean value and is disabled by default. The parameter also accepts the special values required and disabled which were the only supported values before MaxScale 2.3.0.

If enabled, the certificate files mentioned above must also be supplied. MaxScale connections to will then be encrypted with TLS/SSL.


A string giving a file path that identifies an existing readable file. The file must be the SSL client private key MaxScale should use. This is a required parameter for listeners but an optional parameter for servers.


A string giving a file path that identifies an existing readable file. The file must be the SSL client certificate MaxScale should use with the server. The certificate must match the key defined in ssl_key. This is a required parameter for listeners but an optional parameter for servers.


A string giving a file path that identifies an existing readable file. The file must be the Certificate Authority (CA) certificate for the CA that signed the certificate referred to in the previous parameter. It will be used to verify that the certificate is valid. This is a required parameter for both listeners and servers. The CA certificate can consist of a certificate chain.


Note: It is highly recommended to leave this parameter to the default value of MAX. This will guarantee that the strongest available encryption is used. Do not change this unless you know what you are doing.

This parameter controls the level of encryption used. Accepted values are:

  • TLSv10
  • TLSv11
  • TLSv12
  • TLSv13
  • MAX

The default is to use the highest level of encryption available that both the client and server support. MaxScale supports TLSv1.0, TLSv1.1, TLSv1.2 and TLSv1.3 depending on the OpenSSL library version.

The TLSv13 value was added in MaxScale 2.3.15 (MXS-2762).


Set the list of TLS ciphers. By default, no explicit ciphers are defined and the system defaults are used. Note that this parameter does not modify TLSv1.3 ciphers.


The maximum length of the certificate authority chain that will be accepted. The default value is 9, same as the OpenSSL default. The configured value must be larger than 0.


Peer certificate verification. This functionality is disabled by default. In versions prior to 2.3.17 the feature was enabled by default.

When this feature is enabled, the peer must send a certificate. The certificate sent by the peer is verified against the configured Certificate Authority to make sure the peer is who they claim to be. For listeners, this behaves as if REQUIRE X509 was defined for all users. For servers, this behaves like the --ssl-verify-server-cert command line option for the mysql client.

Example SSL enabled server configuration


This example configuration requires all connections to this server to be encrypted with SSL. The paths to the certificate files and the Certificate Authority file are also provided.

Example SSL enabled listener configuration


This example configuration requires all connections to be encrypted with SSL. The paths to the certificate files and the Certificate Authority file are also provided.

Module Types

Routing Modules

The main task of MariaDB MaxScale is to accept database connections from client applications and route the connections or the statements sent over those connections to the various services supported by MariaDB MaxScale.

Currently a number of routing modules are available, these are designed for a range of different needs.

Connection based load balancing: * ReadConnRoute

Read/Write aware statement based router: * ReadWriteSplit

Simple sharding on database level: * SchemaRouter

Binary log server: * Binlogrouter

Monitor Modules

Monitor modules are used by MariaDB MaxScale to internally monitor the state of the backend databases in order to set the server flags for each of those servers. The router modules then use these flags to determine if the particular server is a suitable destination for routing connections for particular query classifications. The monitors are run within separate threads of MariaDB MaxScale and do not affect MariaDB MaxScale's routing performance.

The use of monitors in MaxScale is not absolutely mandatory: it is possible to run MariaDB MaxScale without a monitor module. In this case an external monitoring system must the status of each server via MaxCtrl or the REST API. Only do this if you know what you are doing.

Filter Modules

Filters provide a means to manipulate or process requests as they pass through MariaDB MaxScale between the client side protocol and the query router. A full explanation of each filter's functionality can be found in its documentation.

The Filter Tutorial document shows how you can add a filter to a service and combine multiple filters in one service.

Encrypting Passwords

Passwords stored in the maxscale.cnf file may optionally be encrypted for added security. This is done by creation of an encryption key on installation of MariaDB MaxScale. Encryption keys may be created manually by executing the maxkeys utility with the argument of the filename to store the key. The default location MariaDB MaxScale stores the keys is /var/lib/maxscale. The passwords are encrypted using 256-bit AES CBC encryption.

 # Usage: maxkeys [PATH]
maxkeys /var/lib/maxscale/

Changing the encryption key for MariaDB MaxScale will invalidate any currently encrypted keys stored in the maxscale.cnf file.

Creating Encrypted Passwords

Encrypted passwords are created by executing the maxpasswd command with the location of the .secrets file and the password you require to encrypt as an argument.

# Usage: maxpasswd PATH PASSWORD
maxpasswd /var/lib/maxscale/ MaxScalePw001

The output of the maxpasswd command is a hexadecimal string, this should be inserted into the maxscale.cnf file in place of the ordinary, plain text, password. MariaDB MaxScale will determine this as an encrypted password and automatically decrypt it before sending it the database server.


Runtime Configuration Changes

Read the following documents for different methods of altering the MaxScale configuration at runtime.

All changes to the configuration are persisted as individual configuration files in /var/lib/maxscale/maxscale.cnf.d/. These files are applied after the main configuration file and all auxiliary configurations have been loaded. This means that once runtime configurations have been made, they need to be incorporated into the main configuration files.

Backing Up Configuration Changes

The combination of configuration files can be done either manually (e.g. rsync) or with the maxscale --export-config=FILE command line option. See maxscale --help for more information about how to use the --export-config flag.

For example, to export the current runtime configuration, run the following command.

maxscale --export-config=/tmp/maxscale.cnf.combined

This will create the /tmp/maxscale.cnf.combined file and write the current configuration into the it. This allows new MaxScale instances to be easily set up without requiring copying of all runtime configuration files. The user executing the command must be able to read all MaxScale configuration files as well as create and write the provided filename.

Error Reporting

MariaDB MaxScale is designed to be executed as a service, therefore all error reports, including configuration errors, are written to the MariaDB MaxScale error log file. By default, MariaDB MaxScale will log to a file in /var/log/maxscale and the system log.


The current limitations of MaxScale are listed in the Limitations document.


For a list of common problems and their solutions, read the MaxScale Troubleshooting article on the MariaDB Knowledge Base.


MariaDB uses username, passwords and the client host in order to authenticate a user, so a typical user would be defined as user X at host Y and would be given a password to connect. MariaDB MaxScale uses exactly the same rules as MariaDB when users connect to the MariaDB MaxScale instance, i.e. it will check the address from which the client is connecting and treat this in exactly the same way that MariaDB would. MariaDB MaxScale will pull the authentication data from one of the backend servers (a master server if one is available) and use this to match the incoming connections. MaxScale assumes that all the backend servers for a particular service will share the same set of user credentials.

It is important to understand, however, that when MariaDB MaxScale itself makes connections to the backend servers the backend server will see all connections as originating from the host that runs MariaDB MaxScale and not the original host from which the client connected to MariaDB MaxScale. Therefore the backend servers should be configured to allow connections from the MariaDB MaxScale host for every user that can connect from any host. Since there is only a single password within the database server for a given host, this limits the configuration such that a given user name must have the same password for every host from which they can connect. These limitations do not apply when proxy_protocol is in use.

To clarify, if a user X is defined as using password pass1 from host A and pass2 from host B then there must be an entry in the user table for user X from the MariaDB MaxScale host, say pass1.

This would result in rows in the user table as follows

Username Password Client Host
X pass1 A
X pass2 B
X pass1 MaxScale

In this case the user X would be able to connect to MariaDB MaxScale from host a giving the password of pass1. In addition MariaDB MaxScale would be able to create connections for this user to the backend servers using the username X and password pass1, since the MariaDB MaxScale host is also defined to have password pass1. User X would not however be able to connect from host b since they would need to provide the password pass2 in order to connect to MariaDB MaxScale, but then MariaDB MaxScale would not be able to connect to the backends as it would also use the password pass2 for these connections.

Wildcard Hosts

Hostname mapping in MariaDB MaxScale works in exactly the same way as for MariaDB, if the wildcard is used for the host then any host other than the localhost ( will match. It is important to consider that the localhost check will be performed at the MariaDB MaxScale level and at the MariaDB server level.

If MariaDB MaxScale and the databases are on separate hosts there are two important changes in behavior to consider:

  1. Clients running on the same machine as the backend database now may access the database using the wildcard entry. The localhost check between the client and MariaDB MaxScale will allow the use of the wildcard, since the client is not running on the MariaDB MaxScale host. Also the wildcard entry can be used on the database host as MariaDB MaxScale is making that connection and it is not running on the same host as the database.

  2. Clients running on the same host as MariaDB MaxScale can not access the database via MariaDB MaxScale using the wildcard entry since the connection to MariaDB MaxScale will be from the localhost. These clients are able to access the database directly, as they will use the wildcard entry. This behavior can be configured with the localhost_match_wildcard_host option.

If MariaDB MaxScale is running on the same host as one or more of the database nodes to which it is routing statements then the wildcard host entries can be used to connect to MariaDB MaxScale but not to connect onwards to the database running on the same node.

In all these cases the issue may be solved by adding an explicit entry for the localhost address that has the same password as the wildcard entry. This may be done using a statement as below for each of the databases that are required:

MariaDB [mysql]> GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP ON employee.* 'user1'@'localhost' IDENTIFIED BY 'xxx';
Query OK, 0 rows affected (0.00 sec)

Systemd Watchdog

If MaxScale is running as a systemd service, the systemd Watchdog will be enabled by default. To configure it, change the WatchdogSec option in the Service section of the maxscale systemd configuration file located in /lib/systemd/system/maxscale.service:


It is not recommended to use a watchdog timeout less than 30 seconds. When enabled MaxScale will check that all threads are running and notify systemd with a "keep-alive ping".

Systemd reference:


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