3.8 KiB
MySQL Monitor
Overview
The MySQL Monitor is a monitoring module for MaxScale that monitors a Master-Slave replication cluster. It assigns master and slave roles inside MaxScale according to the actual replication tree in the cluster.
Configuration
A minimal configuration for a monitor requires a set of servers for monitoring and a username and a password to connect to these servers.
[MySQL Monitor]
type=monitor
module=mysqlmon
servers=server1,server2,server3
user=myuser
passwd=mypwd
The user requires the REPLICATION CLIENT privilege to successfully monitor the state of the servers.
MariaDB [(none)]> grant replication client on *.* to 'maxscale'@'maxscalehost';
Query OK, 0 rows affected (0.00 sec)
Optional parameters for all monitors
Here are optional parameters that are common for all the monitors.
monitor_interval
This is the time the monitor waits between each cycle of monitoring. The default value of 10000 milliseconds (10 seconds) should be lowered if you want a faster response to changes in the server states. The value is defined in milliseconds and the smallest possible value is 100 milliseconds.
monitor_interval=2500
backend_connect_timeout
This parameter controls the timeout for connecting to a monitored server. It is in seconds and the minimum value is 1 second. The default value for this parameter is 3 seconds.
backend_connect_timeout=6
backend_write_timeout
This parameter controls the timeout for writing to a monitored server. It is in seconds and the minimum value is 1 second. The default value for this parameter is 2 seconds.
backend_write_timeout=4
backend_read_timeout
This parameter controls the timeout for reading from a monitored server. It is in seconds and the minimum value is 1 second. The default value for this parameter is 1 seconds.
backend_read_timeout=2
MySQL Monitor optional parameters
These are optional parameters specific to the MySQL Monitor.
detect_replication_lag
Detect replication lag between the master and the slaves. This allows the routers to route read queries to only slaves that are up to date.
detect_replication_lag=true
detect_stale_master
Allow previous master to be available even in case of stopped or misconfigured replication. This allows services that depend on master and slave roles to continue functioning as long as the master server is available.
This is a situation which can happen if all slave servers are unreachable or the replication breaks for some reason.
detect_stale_master=true
mysql51_replication
Enable support for MySQL 5.1 replication monitoring. This is needed if a MySQL server older than 5.5 is used as a slave in replication.
mysql51_replication=true
Common Monitor Parameters
For a list of optional parameters that all monitors support, read the Monitor Common document.
Example 1 - Monitor script
Here is an example shell script which sends an email to an admin when a server goes down.
#!/usr/bin/env bash
#This script assumes that the local mail server is configured properly
#The second argument is the event type
event=${$2/.*=/}
server=${$3/.*=/}
message="A server has gone down at `date`."
echo $message|mail -s "The event was $event for server $server." admin@my.org
Here is a monitor configuration that only triggers the script when a master or a slave server goes down.
[Database Monitor]
type=monitor
module=mysqlmon
servers=server1,server2
script=mail_to_admin.sh
events=master_down,slave_down
When a master or a slave server goes down, the script is executed, a mail is sent and the administrator will be immediately notified of any possible problems. This is just a simple example showing what you can do with MaxScale and monitor scripts.