The Ultimate Guide to High Availability with MariaDB

MaxScale 24.02 Binlogrouter

Binlogrouter

The binlogrouter is a router that acts as a replication proxy for MariaDB primary-replica replication. The router connects to a primary, retrieves the binary logs and stores them locally. Replica servers can connect to MaxScale like they would connect to a normal primary server. If the primary server goes down, replication between MaxScale and the replicas can still continue up to the latest point to which the binlogrouter replicated to. The primary can be changed without disconnecting the replicas and without them noticing that the primary server has changed. This allows for a more highly available replication setup.

In addition to the high availability benefits, the binlogrouter creates only one connection to the primary whereas with normal replication each individual replica will create a separate connection. This reduces the amount of work the primary database has to do which can be significant if there are a large number of replicating replicas.

Binlog purge, archive and compress

File purge and archive are mutually exclusive. Archiving simply means that a binlog is moved to another directory. That directory can be mounted to another file system for backups or, for example, a locally mounted S3 bucket.

If archiving is started from a primary that still has all its history intact, a full copy of the primary can be archived.

File compression preserves disk space and makes archiving faster. All binlogs except the very last one, which is the one being logged to, can be compressed. The overhead of reading from a compressed binlog is small, and is typically only needed when a replica goes down, reconnects and is far enough behind the current GTID that an older file needs to be opened.

There is no automated way as of yet for the binlogrouter to use archived files, but should the need arise files can be copied from the archive to the binlog directory. See 'Modifying binlog files manually'.

The related configuration options, which are explained in more detail in the configuration section are: expiration_mode Select purge or archive. datadir Directory where binlog files are stored (the default is usually fine). archivedir Directory to which files are archived. This directory must exist when MaxScale is started. expire_log_minimum_files The minimum number of binlogs to keep before purge or archive is allowed. expire_log_duration Duration from the last file modification until the binlog is eligible for purge or archive. compression_algorithm Select a compression algorithm or none for no compression. Currently only zstandard is supported. * number_of_noncompressed_files The minimum number of binlogs not to compress.

Following are example settings where it is expected that a replica is down for no more than 24 hours.

expiration_mode=archive
archivedir = /mnt/binlog-s3
expire_log_minimum_files=3
expire_log_duration=24h
compression_algorithm=zstandard
number_of_noncompressed_files=2

Modifying binlog files manually

There is usually no reason to modify the contents of the binlog directory. Changing the contents can cause failures if not done correctly. Never make any changes if running a version prior to 23.08, except when a bootstrap is needed.

A binlog file has the name <basename>.<sequence_number>. The basename is decided by the primary server. The sequence number increases by one for each file and is six digits long. The first file has the name <basename>.000001

The file binlog.index contains the view of the current state of the binlogs as a list of file names ordered by the file sequence number. binlog.index is automatically generated any time the contents of datadir changes.

Older files can be manually deleted and should be deleted in the order they were created, lowest to highest sequence number. Prefer to use purge configuration.

Archived files can be copied back to datadir, but care should be taken to copy them back in the reverse order they were created, highest to lowest sequence number. The copied over files will be re-archived once expire_log_duration time has passed.

Never leave a gap in the sequence numbers, and always preserve the name of a binlog file if copied. Do not copy binlog files on top of existing binlog files.

As of version 24.02 any binlog except the latest one can be manually compressed, .e.g:

zstd --rm -z binlog.001234

Supported SQL Commands

The binlogrouter supports a subset of the SQL constructs that the MariaDB server supports. The following commands are supported:

  • CHANGE MASTER TO

  • The binlogrouter supports the same syntax as the MariaDB server but only the following values are allowed:

    • MASTER_HOST
    • MASTER_PORT
    • MASTER_USER
    • MASTER_PASSWORD
    • MASTER_USE_GTID
    • MASTER_SSL
    • MASTER_SSL_CA
    • MASTER_SSL_CAPATH
    • MASTER_SSL_CERT
    • MASTER_SSL_CRL
    • MASTER_SSL_CRLPATH
    • MASTER_SSL_KEY
    • MASTER_SSL_CIPHER
    • MASTER_SSL_VERIFY_SERVER_CERT

    NOTE: MASTER_LOG_FILE and MASTER_LOG_POS are not supported as binlogrouter only supports GTID based replication.

  • STOP SLAVE

  • Stops replication, same as MariaDB.

  • START SLAVE

  • Starts replication, same as MariaDB.

  • RESET SLAVE

  • Resets replication. Note that the RESET SLAVE ALL form that is supported by MariaDB isn't supported by the binlogrouter.

  • SHOW BINARY LOGS

  • Lists the current files and their sizes. These will be different from the ones listed by the original primary where the binlogrouter is replicating from.

  • PURGE { BINARY | MASTER } LOGS TO <filename>

  • Purges binary logs up to but not including the given file. The file name must be one of the names shown in SHOW BINARY LOGS. The version of this command which accepts a timestamp is not currently supported. Automatic purging is supported using the configuration parameter expire_log_duration.

    The files are purged in the order they were created. If a file to be purged is detected to be in use, the purge stops. This means that the purge will stop at the oldest file that a replica is still reading.

    NOTE: You should still take precaution not to purge files that a potential replica will need in the future. MaxScale can only detect that a file is in active use when a replica is connected, and requesting events from it.

  • SHOW MASTER STATUS

  • Shows the name and position of the file to which the binlogrouter will write the next replicated data. The name and position do not correspond to the name and position in the primary.

  • SHOW SLAVE STATUS

  • Shows the replica status information similar to what a normal MariaDB replica server shows. Some of the values are replaced with constants values that never change. The following values are not constant:

    • Slave_IO_State: Set to Waiting for primary to send event when replication is ongoing.

    • Master_Host: Address of the current primary.

    • Master_User: The user used to replicate.

    • Master_Port: The port the primary is listening on.

    • Master_Log_File: The name of the latest file that the binlogrouter is writing to.

    • Read_Master_Log_Pos: The current position where the last event was written in the latest binlog.

    • Slave_IO_Running: Set to Yes if replication running and No if it's not.

    • Slave_SQL_Running Set to Yes if replication running and No if it's not.

    • Exec_Master_Log_Pos: Same as Read_Master_Log_Pos.

    • Gtid_IO_Pos: The latest replicated GTID.

  • SELECT { Field } ...

  • The binlogrouter implements a small subset of the MariaDB SELECT syntax as it is mainly used by the replicating replicas to query various parameters. If a field queried by a client is not known to the binlogrouter, the value will be returned back as-is. The following list of functions and variables are understood by the binlogrouter and are replaced with actual values:

    • @@gtid_slave_pos, @@gtid_current_pos or @@gtid_binlog_pos: All of these return the latest GTID replicated from the primary.

    • version() or @@version: The version string returned by MaxScale when a client connects to it.

    • UNIX_TIMESTAMP(): The current timestamp.

    • @@version_comment: Always pinloki.

    • @@global.gtid_domain_id: Always 0.

    • @master_binlog_checksum: Always CRC32.

    • @@session.auto_increment_increment: Always 1

    • @@character_set_client: Always utf8

    • @@character_set_connection: Always utf8

    • @@character_set_results: Always utf8

    • @@character_set_server: Always utf8mb4

    • @@collation_server: Always utf8mb4_general_ci

    • @@collation_connection: Always utf8_general_ci

    • @@init_connect: Always an empty string

    • @@interactive_timeout: Always 28800

    • @@license: Always BSL

    • @@lower_case_table_names: Always 0

    • @@max_allowed_packet: Always 16777216

    • @@net_write_timeout: Always 60

    • @@performance_schema: Always 0

    • @@query_cache_size: Always 1048576

    • @@query_cache_type: Always OFF

    • @@sql_mode: Always an empty string

    • @@system_time_zone: Always UTC

    • @@time_zone: Always SYSTEM

    • @@tx_isolation: Always REPEATABLE-READ

    • @@wait_timeout: Always 28800

  • SET

  • @@global.gtid_slave_pos: Set the position from which binlogrouter should start replicating. E.g. SET @@global.gtid_slave_pos="0-1000-1234,1-1001-5678"

  • SHOW VARIABLES LIKE '...'

  • Shows variables matching a string. The LIKE operator in SHOW VARIABLES is mandatory for the binlogrouter. This means that a plain SHOW VARIABLES is not currently supported. In addition, the LIKE operator in binlogrouter only supports exact matches.

    Currently the only variables that are returned are gtid_slave_pos, gtid_current_pos and gtid_binlog_pos which return the current GTID coordinates of the binlogrouter. In addition to these, the server_id variable will return the configured server ID of the binlogrouter.

Semi-sync replication

If the server from which the binlogrouter replicates from is using semi-sync replication, the binlogrouter will acknowledge the replicated events.

Configuration Parameters

The binlogrouter is configured similarly to how normal routers are configured in MaxScale. It requires at least one listener where clients can connect to and one server from which the database user information can be retrieved. An example configuration can be found in the example section of this document.

datadir

  • Type: path
  • Mandatory: No
  • Dynamic: No
  • Default: /var/lib/maxscale/binlogs

Directory where binary log files are stored.

archivedir

  • Type: string
  • Mandatory: Yes
  • Default: No
  • Dynamic: No

Mandatory if expiration_mode=archive

The directory to where files are archived. This is presumably a directory mounted to a remote file system or an S3 bucket. Ensure that the user running MaxScale (typically "maxscale") has sufficient privileges on the archive directory. S3 buckets mounted with s3fs may require setting permissions manually:

s3fs my-bucket /home/joe/S3_bucket_mount/ -o umask=0077

The directory must exist when MaxScale starts.

server_id

  • Type: count
  • Mandatory: No
  • Dynamic: No
  • Default: 1234

The server ID that MaxScale uses when connecting to the primary and when serving binary logs to the replicas.

net_timeout

  • Type: duration
  • Mandatory: No
  • Dynamic: No
  • Default: 10s

Network connection and read timeout for the connection to the primary.

select_master

  • Type: boolean
  • Mandatory: No
  • Dynamic: No
  • Default: false

Automatically select the primary server to replicate from.

When this feature is enabled, the primary which binlogrouter will replicate from will be selected from the servers defined by a monitor cluster=TheMonitor. Alternatively servers can be listed in servers. The servers should be monitored by a monitor. Only servers with the Master status are used. If multiple primary servers are available, the first available primary server will be used.

If a CHANGE MASTER TO command is received while select_master is on, the command will be honored and select_master turned off until the next reboot. This allows the Monitor to perform failover, and more importantly, switchover. It also allows the user to manually redirect the Binlogrouter. The current primary is "sticky", meaning that the same primary will be chosen on reboot.

NOTE: Do not use the mariadbmon parameter auto_rejoin if the monitor is monitoring a binlogrouter. The binlogrouter does not support all the SQL commands that the monitor will send and the rejoin will fail. This restriction will be lifted in a future version.

The GTID the replication will start from, will be based on the latest replicated GTID. If no GTID has been replicated, the router will start replication from the start. Manual configuration of the GTID can be done by first configuring the replication manually with CHANGE MASTER TO.

expiration_mode

  • Type: enum
  • Dynamic: No
  • Values: purge, archive
  • Default: purge

Choose whether expired logs should be purged or archived.

expire_log_duration

  • Type: duration
  • Mandatory: No
  • Dynamic: No
  • Default: 0s

Duration after which a binary log file expires, i.e. becomes eligible for purge or archive. This is similar to the server system variable.

A value of 0s turns off purging.

expire_log_days.

The duration is measured from the last modification of the log file. Files are purged in the order they were created. The automatic purge works in a similar manner to PURGE BINARY LOGS TO <filename> in that it will stop the purge if an eligible file is in active use, i.e. being read by a replica.

expire_log_minimum_files

  • Type: number
  • Mandatory: No
  • Dynamic: No
  • Default: 2

The minimum number of log files the automatic purge keeps. At least one file is always kept.

compression_algorithm

  • Type: enum
  • Mandatory: No
  • Dynamic: No
  • Values: none, zstandard
  • Default: none

number_of_noncompressed_files

  • Type: count
  • Mandatory: No
  • Dynamic: No
  • Default: 2

The minimum number of log files that are not compressed. At least one file is not compressed.

ddl_only

  • Type: boolean
  • Mandatory: No
  • Dynamic: No
  • Default: false

When enabled, only DDL events are written to the binary logs. This means that CREATE, ALTER and DROP events are written but INSERT, UPDATE and DELETE events are not.

This mode can be used to keep a record of all the schema changes that occur on a database. As only the DDL events are stored, it becomes very easy to set up an empty server with no data in it by simply pointing it at a binlogrouter instance that has ddl_only enabled.

encryption_key_id

  • Type: string
  • Mandatory: No
  • Dynamic: No
  • Default: ""

Encryption key ID used to encrypt the binary logs. If configured, an Encryption Key Manager must also be configured and it must contain the key with the given ID. If the encryption key manager supports versioning, new binary logs will be encrypted using the latest encryption key. Old binlogs will remain encrypted with older key versions and remain readable as long as the key versions used to encrypt them are available.

Once binary log encryption has been enabled, the encryption key ID cannot be changed and the key must remain available to MaxScale in order for replication to work. If an encryption key is not available or the key manager fails to retrieve it, the replication from the currently selected primary server will stop. If the replication is restarted manually, the encryption key retrieval is attempted again.

Re-encryption of binlogs using another encryption key is not possible. However, this is possible if the data is replicated to a second MaxScale server that uses a different encryption key. The same approach can also be used to decrypt binlogs.

encryption_cipher

  • Type: enum
  • Mandatory: No
  • Dynamic: No
  • Values: AES_CBC, AES_CTR, AES_GCM
  • Default: AES_GCM

The encryption cipher to use. The encryption key size also affects which mode is used: only 128, 192 and 256 bit encryption keys are currently supported.

Possible values are:

rpl_semi_sync_slave_enabled

  • Type: boolean
  • Mandatory: No
  • Default: false
  • Dynamic: Yes

Enable semi-synchronous replication when replicating from a MariaDB server. If enabled, the binlogrouter will send acknowledgment for each received event. Note that the rpl_semi_sync_master_enabled parameter must be enabled in the MariaDB server where the replication is done from for the semi-synchronous replication to take place.

New installation

  1. Configure and start MaxScale.

  2. If you have not configured select_master=true (automatic primary selection), issue a CHANGE MASTER TO command to binlogrouter.

mariadb -u USER -pPASSWORD -h maxscale-IP -P binlog-PORT
CHANGE MASTER TO master_host="primary-IP", master_port=primary-PORT, master_user=USER, master_password="PASSWORD", master_use_gtid=slave_pos;
START SLAVE;
  1. Redirect each replica to replicate from Binlogrouter
mariadb -u USER -pPASSWORD -h replica-IP -P replica-PORT
STOP SLAVE;
CHANGE MASTER TO master_host="maxscale-IP", master_port=binlog-PORT,
master_user="USER", master_password="PASSWORD", master_use_gtid=slave_pos;
START SLAVE;
SHOW SLAVE STATUS \G

Upgrading from legacy versions

Binlogrouter does not read any of the data that a version prior to 2.5 has saved. By default binlogrouter will request the replication stream from the blank state (from the start of time), which is basically meant for new systems. If a system is live, the entire replication data probably does not exist, and if it does, it is not necessary for binlogrouter to read and store all the data.

Before you start

  • Note that binlogrouter only supports GTID based replication.
  • Make sure that the configured data directory for the new binlogrouter is different from the old one, or move old data away. See datadir.
  • If the primary contains binlogs from the blank state, and there is a large amount of data, consider purging old binlogs. See Using and Maintaining the Binary Log.

Deployment

The method described here inflicts the least downtime. Assuming you have configured MaxScale version 2.5 or newer, and it is ready to go:

  1. Redirect each replica that replicates from Binlogrouter to replicate from the primary.
mariadb -u USER -pPASSWORD -h replica-IP -P replica-PORT
STOP SLAVE;
CHANGE MASTER TO master_host="master-IP", master_port=master-PORT,
master_user="USER", master_password="PASSWORD", master_use_gtid=slave_pos;
START SLAVE;
SHOW SLAVE STATUS \G

  1. Stop the old version of MaxScale, and start the new one. Verify routing functionality.

  2. Issue a CHANGE MASTER TO command, or use select_master.

mariadb -u USER -pPASSWORD -h maxscale-IP -P binlog-PORT
CHANGE MASTER TO master_host="primary-IP", master_port=primary-PORT,
master_user=USER,master_password="PASSWORD", master_use_gtid=slave_pos;
  1. Run maxctrl list servers. Make sure all your servers are accounted for. Pick the lowest gtid state (e.g. 0-1000-1234,1-1001-5678) on display and issue this command to Binlogrouter:
STOP SLAVE
SET @@global.gtid_slave_pos = "0-1000-1234,1-1001-5678";
START SLAVE

NOTE: Even with select_master=true you have to set @@global.gtid_slave_pos if any binlog files have been purged on the primary. The server will only stream from the start of time if the first binlog file is present. See select_master.

  1. Redirect each replica to replicate from Binlogrouter.
mariadb -u USER -pPASSWORD -h replica-IP -P replica-PORT
STOP SLAVE;
CHANGE MASTER TO master_host="maxscale-IP", master_port=binlog-PORT,
master_user="USER", master_password="PASSWORD",
master_use_gtid=slave_pos;
START SLAVE;
SHOW SLAVE STATUS \G

Bootstrap binlogrouter

If for any reason you need to "bootstrap" the binlogrouter you can change the datadir or delete the entire binglog directory (datadir) when MaxScale is NOT running. This could be necessary if files are accidentally deleted or the file system becomes corrupt.

No changes are required to the attached replicas.

if select_master is set to true and the primary contains the entire binlog history, a simple restart of MaxScale sufficies.

In the normal case, the primary does not have the entire history and you will need to set the GTID position to a starting value, usually the earliest gtid state of all replicas. Once MaxScale has been restarted connect to the binlogrouter from the command line.

If select_master is set to true issue:

mariadb -u USER -pPASSWORD -h maxscale-IP -P binlog-PORT
STOP SLAVE;
SET @@global.gtid_slave_pos = "gtid_state";
START SLAVE;

else

mariadb -u USER -pPASSWORD -h maxscale-IP -P binlog-PORT
CHANGE MASTER TO master_host="primary-IP", master_port=primary-PORT, master_user=USER, master_password="PASSWORD", master_use_gtid=slave_pos;
SET @@global.gtid_slave_pos = "gtid_state";
START SLAVE;

Galera cluster

When replicating from a Galera cluster, select_master must be set to true, and the servers must be monitored by the Galera Monitor. Configuring binlogrouter is the same as described above.

The Galera cluster must be configured to use Wsrep GTID Mode.

The MariaDB version must be 10.5.1 or higher. The required GTID related server settings for MariaDB/Galera to work with Binlogrouter are listed here:

[mariadb]
log_slave_updates = ON
log_bin = pinloki       # binlog file base name. Must be the same on all servers
gtid_domain_id = 1001   # Must be different for each galera server
binlog_format = ROW

[galera]
wsrep_on = ON
wsrep_gtid_mode = ON
wsrep_gtid_domain_id = 42  # Must be the same for all servers

Example

The following is a small configuration file with automatic primary selection. With it, the service will accept connections on port 3306.

[server1]
type=server
address=192.168.0.1
port=3306

[server2]
type=server
address=192.168.0.2
port=3306

[MariaDB-Monitor]
type=monitor
module=mariadbmon
servers=server1, server2
user=maxuser
password=maxpwd
monitor_interval=10s

[Replication-Proxy]
type=service
router=binlogrouter
cluster=MariaDB-Monitor
select_master=true
expiration_mode=archive
archivedir=/mnt/somedir
expire_log_minimum_files=3
expire_log_duration=24h
compression_algorithm=zstandard
number_of_noncompressed_files=2
user=maxuser
password=maxpwd

[Replication-Listener]
type=listener
service=Replication-Proxy
port=3306

Limitations

  • Old-style replication with binlog name and file offset is not supported and the replication must be started by setting up the GTID to replicate from.

  • Only replication from MariaDB servers (including Galera) is supported.

  • Old encrypted binary logs are not re-encrypted with newer key versions (MXS-4140)

  • The MariaDB server where the replication is done from must be configured with binlog_checksum=CRC32.

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