MaxScale/Documentation/Monitors/Clustrix-Monitor.md

Clustrix Monitor

Overview

The Clustrix Monitor is a monitor that monitors a Clustrix cluster. It is capable of detecting the cluster setup and creating corresponding server instances within MaxScale.

Configuration

A minimal configuration for a monitor requires one server in the Clustrix cluster, and a username and a password to connect to the server. Note that the Clustrix monitor will only use that server in order to dynamically find out the configuration of the cluster; after startup it will completely rely upon information obtained at runtime.

To ensure that the Clustrix monitor will be able to start, it is adviseable to provide more than one server to cater for the case that not all nodes are always up when MaxScale starts.

[TheClustrixMonitor]
type=monitor
module=clustrixmon
servers=server1,server2,server3
user=myuser
password=mypwd

Dynamic Servers

The server objects the Clustrix monitor creates for each detected Clustrix node will be named like

@@<name-of-clustrix-monitor>:node-<id>

where <name-of-clustrix-monitor> is the name of the Clustrix monitor instance, as defined in the MaxScale configuration file, and <id> is the id of the Clustrix node.

For instance, with the Clustrix monitor defined as above and a Clustrix cluster consisting of 3 nodes whose ids are 1, 2 and 3 respectively, the names of the created server objects will be:

@@TheClustrixMonitor:node-1
@@TheClustrixMonitor:node-2
@@TheClustrixMonitor:node-3

Grants

Note that the monitor user must have SELECT grant on the following tables:

• system.nodeinfo
• system.membership
• system.softfailed_nodes

You can give the necessary grants using the following commands:

    GRANT SELECT ON system.membership TO 'myuser'@'%';
    GRANT SELECT ON system.nodeinfo TO 'myuser'@'%';
    GRANT SELECT ON system.softfailed_nodes TO 'myuser'@'%';

Further, if you want be able to softfail and unsoftfail a node via MaxScale, then the monitor user must have SUPER privileges, which can be granted like:

    GRANT SUPER ON *.* TO 'myuser'@'%';

The user name must be changed to the one actually being used.

Common Monitor Parameters

For a list of optional parameters that all monitors support, read the Monitor Common document.

Clustrix Monitor optional parameters

These are optional parameters specific to the Clustrix Monitor.

cluster_monitor_interval

Defines, in milliseconds, how often the monitor checks the state of the entire cluster. The default value is 60000 (1 minute), which should not be lowered as that may have an adverse effect on the Cluster itself.

cluster_monitor_interval=120000

health_check_threshold

Defines how many times the health check may fail before the monitor considers a particular node to be down. The default value is 2.

health_check_threshold=3

Commands

The Clustrix monitor supports the following module commands.

softfail

With the softfail module command, a node can be softfailed via MaxScale. The command requires as argument the name of the Clustrix monitor instance (as defined in the configuration file) and the name of the node to be softfailed.

For instance, with a configuration file like

[TheClustrixMonitor]
type=monitor
module=clustrixmon
...

then the node whose server name is @@TheClustrixMonitor:node-1 can be softfailed like

$ maxctrl call command clustrixmon softfail TheClustrixMonitor @@TheClustrixMonitor:node-1

If a node is successfully softfailed, then the status of the corresponding MaxScale server object will be set to Being Drained, which will prevent new connections from being created to the node.

unsoftfail

With the unsoftfail module command, a node can be unsoftfailed via MaxScale. The command requires as argument the name of the Clustrix monitor instance (as defined in the configuration file) and the name of the node to be unsoftfailed.

With a setup similar to the softfail case, a node can be unsoftfailed like:

$ maxctrl call command clustrixmon unsoftfail TheClustrixMonitor @@TheClustrixMonitor:node-1

If a node is successfully softfailed, then a Being Drained status of the corresponding MaxScale server object will be cleared.

SOFTFAILed nodes

During the cluster check, which is performed once per cluster_monitor_interval, the monitor will also check whether any nodes are being softfailed. The status of the corresponding server object of a node being softfailed will be set to Being Drained, which will prevent new connections from being created to that node.

If a node that was softfailed is UNSOFTFAILed then the Being Drained status will be cleared.

If the softfailing and unsoftfailing is initiated using the softfail and unsoftfail commands of the Clustrix monitor, then there will be no delay between the softfailing or unsoftfailing being initated and the Being Drained status being turned on/off.