REST API Tutorial

REST API Tutorial

This tutorial is a quick overview of what the MaxScale REST API offers, how it can be used to inspect the state of MaxScale and how to use it to modify the runtime configuration of MaxScale. The tutorial uses the curl command line client to demonstrate how the API is used.

Configuration and Hardening

The MaxScale REST API listens on port 8989 on the local host. The admin_port and admin_host parameters control which port and address the REST API listens on. Note that for security reasons the API only listens for local connections with the default configuration. It is critical that the default credentials are changed and TLS/SSL encryption is configured before exposing the REST API to a network.

The default user for the REST API is admin and the password is mariadb. The easiest way to secure the REST API is to use the maxctrl command line client to create a new admin user and delete the default one. To do this, run the following commands:

maxctrl create user my_user my_password --type=admin
maxctrl destroy user admin

This will create the user my_user with the password my_password that is an administrative account. After this account is created, the default admin account is removed with the next command.

The next step is to enable TLS encryption. To do this, you need a CA certificate, a private key and a public certificate file all in PEM format. Add the following three parameters under the [maxscale] section of the MaxScale configuration file and restart MaxScale.

admin_ssl_key=/certs/server-key.pem
admin_ssl_cert=/certs/server-cert.pem
admin_ssl_ca_cert=/certs/ca-cert.pem

Use maxctrl to verify that the TLS encryption is enabled. In this tutorial our server certificates are self-signed so the --tls-verify-server-cert=false option is required.

maxctrl --user=my_user --password=my_password --secure --tls-ca-cert=/certs/ca-cert.pem --tls-verify-server-cert=false show maxscale

If no errors are raised, this means that the communication via the REST API is now secure and can be used across networks.

Requesting Data

Note: For the sake of brevity, the rest of this tutorial will omit the TLS/SSL options from the curl command line. For more information, refer to the curl manpage.

The most basic task to do with the REST API is to see whether MaxScale is up and running. To do this, we do a HTTP request on the root resource (the -i option shows the HTTP headers).

curl -i 127.0.0.1:8989/v1/

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Length: 0
Last-Modified: Mon, 04 Mar 2019 08:23:09 GMT
ETag: "0"
Date: Mon, 04 Mar 19 08:29:41 GMT

To query a resource collection endpoint, append it to the URL. The /v1/filters/ endpoint shows the list of filters configured in MaxScale. This is a resource collection endpoint: it contains the list of all resources of a particular type.

curl 127.0.0.1:8989/v1/filters

{
    "links": {
        "self": "http://127.0.0.1:8989/v1/filters/"
    },
    "data": [
        {
            "id": "Hint",
            "type": "filters",
            "relationships": {
                "services": {
                    "links": {
                        "self": "http://127.0.0.1:8989/v1/services/"
                    },
                    "data": [
                        {
                            "id": "RW-Split-Hint-Router",
                            "type": "services"
                        }
                    ]
                }
            },
            "attributes": {
                "module": "hintfilter",
                "parameters": {}
            },
            "links": {
                "self": "http://127.0.0.1:8989/v1/filters/Hint"
            }
        },
        {
            "id": "Logger",
            "type": "filters",
            "relationships": {
                "services": {
                    "links": {
                        "self": "http://127.0.0.1:8989/v1/services/"
                    },
                    "data": []
                }
            },
            "attributes": {
                "module": "qlafilter",
                "parameters": {
                    "match": null,
                    "exclude": null,
                    "user": null,
                    "source": null,
                    "filebase": "/tmp/log",
                    "options": "ignorecase",
                    "log_type": "session",
                    "log_data": "date,user,query",
                    "newline_replacement": "\" \"",
                    "separator": ",",
                    "flush": false,
                    "append": false
                },
                "filter_diagnostics": {
                    "separator": ",",
                    "newline_replacement": "\" \""
                }
            },
            "links": {
                "self": "http://127.0.0.1:8989/v1/filters/Logger"
            }
        }
    ]
}

The data holds the actual list of resources: the Hint and Logger filters. Each object has the id field which is the unique name of that object. It is the same as the section name in maxscale.cnf.

Each resource in the list has a relationships object. This shows the relationship links between resources. In our example, the Hint filter is used by a service named RW-Split-Hint-Router and the Logger is not currently in use.

To request an individual resource, we add the object name to the resource collection URL. For example, if we want to get only the Logger filter we execute the following command.

curl 127.0.0.1:8989/v1/filters/Logger

{
    "links": {
        "self": "http://127.0.0.1:8989/v1/filters/Logger"
    },
    "data": {
        "id": "Logger",
        "type": "filters",
        "relationships": {
            "services": {
                "links": {
                    "self": "http://127.0.0.1:8989/v1/services/"
                },
                "data": []
            }
        },
        "attributes": {
            "module": "qlafilter",
            "parameters": {
                "match": null,
                "exclude": null,
                "user": null,
                "source": null,
                "filebase": "/tmp/log",
                "options": "ignorecase",
                "log_type": "session",
                "log_data": "date,user,query",
                "newline_replacement": "\" \"",
                "separator": ",",
                "flush": false,
                "append": false
            },
            "filter_diagnostics": {
                "separator": ",",
                "newline_replacement": "\" \""
            }
        },
        "links": {
            "self": "http://127.0.0.1:8989/v1/filters/Logger"
        }
    }
}

Note that this time the data member holds an object instead of an array of objects. All other parts of the response are similar to what was shown in the previous example.

Creating Objects

One of the uses of the REST API is to create new objects in MaxScale at runtime. This allows new servers, services, filters, monitor and listeners to be created without restarting MaxScale.

For example, to create a new server in MaxScale the JSON definition of a server must be sent to the REST API at the /v1/servers/ endpoint. The request body defines the server name as well as the parameters for it.

To create objects with curl, first write the JSON definition into a file.

{
    "data": {
        "id": "server1",
        "type": "servers",
        "attributes": {
            "parameters": {
                "address": "127.0.0.1",
                "port": 3003
            }
        }
    }
}

To send the data, use the following command.

curl -X POST -d @new_server.txt 127.0.0.1:8989/v1/servers

The -d option takes a file name prefixed with a @ as an argument. Here we have @new_server.txt which is the name of the file where the JSON definition was stored. The -X option defines the HTTP verb to use and to create a new object we must use the POST verb.

To verify the data request the newly created object.

curl 127.0.0.1:8989/v1/servers/server1

Modifying Data

The easiest way to modify an object is to first request it, store the result in a file, edit it and then send the updated object back to the REST API.

Let's say we want to modify the port that the server we created earlier listens on. First we request the current object and store the result in a file.

curl 127.0.0.1:8989/v1/servers/server1 > server1.txt

After that we edit the file and change the port from 3003 to 3306. Next the modified JSON object is sent to the REST API as a PATCH command. To do this, execute the following command.

curl -X PATCH -d @server1.txt 127.0.0.1:8989/v1/servers/server1

To verify that the data was updated correctly, request the updated object.

curl 127.0.0.1:8989/v1/servers/server1

Object Relationships

To continue with our previous example, we add the updated server to a service. To do this, the relationships object of the server must be modified to include the service we want to add the server to.

To define a relationship between a server and a service, the data member must have the relationships field and it must contain an object with the services field (some fields omitted for brevity).

{
    "data": {
        "id": "server1",
        "type": "servers",
        "relationships": {
            "services": {
                "data": [
                    {
                        "id": "RW-Split-Router",
                        "type": "services"
                    }
                ]
            }
        },
        "attributes":  ...
    }
}

The data.relationships.services.data field contains a list of objects that define the id and type fields. The id is the name of the object (a service or a monitor for servers) and the type tells which type it is. Only services type objects should be present in the services object.

In our example we are linking the server1 server to the RW-Split-Router service. As was seen with the previous example, the easiest way to do this is to store the result, edit it and then send it back with a HTTP PATCH.

If we want to remove a server from all services, we can set the relationships field to {}. The REST API interprets this as an instruction to remove the server from all services and monitors. This is useful if you want to delete the server which can only be done if it has no relationships to other objects.

Deleting Objects

To delete an object, simply execute a HTTP DELETE request on the resource you want to delete. For example, to delete the server1 server, execute the following command.

curl -X DELETE 127.0.0.1:8989/v1/servers/server1

Further Reading

The full list of all available endpoints in MaxScale can be found in the REST API documentation.

The maxctrl command line client is self-documenting and the maxctrl help command is a good tool for exploring the various commands that are available in it. The maxctrl api get command can be useful way to explore the REST API as it provides a way to easily extract values out of the JSON data generated by the REST API.

There is a multitude of REST API clients readily available and most of them are far more convenient to use than curl. We recommend investigating what you need and how you intend to either integrate or use the MaxScale REST API. Most modern languages either have a built-in HTTP library or there exists a de facto standard library.

The MaxScale REST API follows the JSON API specification and there exist libraries that are built specifically for these sorts of APIs

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