4.5 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. The user requires the REPLICATION CLIENT privilege to successfully monitor the state of the servers.
[MySQL Monitor]
type=monitor
module=mysqlmon
servers=server1,server2,server3
user=myuser
passwd=mypwd
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
script
This script will be executed when a server changes its state. The parameter should be an absolute path to the script or it should be in the executable path.
script=/home/user/script.sh
This script will be called with the following command line arguments.
<name of the script> --event=<event type> --initiator=<server whose state changed> --nodelist=<list of all servers>
events
A list of event names which cause the script to be executed. If this option is not defined, all events cause the script to be executed. The list must contain a comma separated list of event names.
events=master_down,slave_down
Script events
Here is a table of all possible event types and their descriptions.
| Event Name | Description |
|---|---|
| master_down | A Master server has gone down |
| master_up | A Master server has come up |
| slave_down | A Slave server has gone down |
| slave_up | A Slave server has come up |
| server_down | A server with no assigned role has gone down |
| server_up | A server with no assigned role has come up |
| lost_master | A server lost Master status |
| lost_slave | A server lost Slave status |
| new_master | A new Master was detected |
| new_slave | A new Slave was detected |
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.