Percona Clustercheck

Script to make a proxy (ie HAProxy) capable of monitoring Percona XtraDB Cluster nodes properly.

Usage

Below is a sample configuration for HAProxy on the client. The point of this is that the application will be able to connect to localhost port 3307, so although we are using Percona XtraDB Cluster with several nodes, the application will see this as a single MySQL server running on localhost.

/etc/haproxy/haproxy.cfg

...
listen percona-cluster 0.0.0.0:3307
  balance leastconn
  option httpchk
  mode tcp
    server node1 1.2.3.4:3306 check port 9200 inter 5000 fastinter 2000 rise 2 fall 2
    server node2 1.2.3.5:3306 check port 9200 inter 5000 fastinter 2000 rise 2 fall 2
    server node3 1.2.3.6:3306 check port 9200 inter 5000 fastinter 2000 rise 2 fall 2 backup

MySQL connectivity is checked via HTTP on port 9200. The clustercheck script is a simple shell script which accepts HTTP requests and checks MySQL on an incoming request. If the Percona XtraDB Cluster node is ready to accept requests, it will respond with HTTP code 200 (OK), otherwise a HTTP error 503 (Service Unavailable) is returned.

Setup

This setup will create a process that listens on TCP port 9200 using xinetd. This process uses the clustercheck script from this repository to report the status of the node.

First, create a clustercheckuser that will be doing the checks.

mysql> GRANT PROCESS ON *.* TO 'clustercheckuser'@'localhost' IDENTIFIED BY 'clustercheckpassword!'

Copy the clustercheck from the repository to a location (/usr/bin in the example below) and make it executable. Then add the following service to xinetd (make sure to match your location of the script with the 'server'-entry).

/etc/xinetd.d/mysqlchk:

# default: on
# description: mysqlchk
service mysqlchk
{
        disable = no
        flags = REUSE
        socket_type = stream
        port = 9200
        wait = no
        user = nobody
        server = /usr/bin/clustercheck
        log_on_failure += USERID
        only_from = 0.0.0.0/0
        per_source = UNLIMITED
}

Also, you should add the mysqlchk service to /etc/services before restarting xinetd.

xinetd      9098/tcp    # ...
mysqlchk    9200/tcp    # MySQL check  <--- Add this line
git         9418/tcp    # Git Version Control System
zope        9673/tcp    # ...

Clustercheck will now listen on port 9200 after xinetd restart, and HAproxy is ready to check MySQL via HTTP poort 9200.

Options

The clustercheck script contains a couple of variables and options.

• MYSQL_USERNAME and MYSQL_PASSWORD: defines the username and password for the check
• ERR_FILE (default "/dev/null"): defines where errors from the checks should go
• AVAILABLE_WHEN_DONOR (default 0): By default, the node is reported unavailable if it’s a donor for SST. If you want to allow queries on a node which is a donor for SST, you can set this variable to 1. Note: when you set this variable to 1, you will also need to use a non-blocking SST method like xtrabackup