MaxScale 21.06 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 and monitors, we can set the
data member of the services and monitors relationships to an empty array:
{
"data": {
"relationships": {
"services": {
"data": []
},
"monitors": {
"data": []
}
}
}
}
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
In order to delete an object, it must not have any relationships to other objects.
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
