# 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 acutal replication tree in the cluster. ## Configuration A minimal configuration of the MySQL 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 Here are optional parameters for the MySQL monitor that change the way it behaves. ### `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 illiseconds. ``` 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 ``` ### `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. ``` --event= --node= --nodelist= ``` Here is a table of all possible event names 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 done down server_up|A server with no assigned role has come up synced_down|A synced Galera node has come up synced_up|A synced Galera node has gone down donor_down|A donor Galera node has come up donor_up|A donor Galera node has gone down ndb_down|A MySQL Cluster node has gone down ndb_up|A MySQL Cluster node has come up lost_master|A server lost Master status lost_slave|A server lost Slave status lost_synced|A Galera node lost synced status lost_donor|A Galera node lost donor status lost_ndb|A MySQL Cluster node lost node membership new_master|A new Master was detected new_slave|A new Slave was detected new_synced|A new synced Galera node was detected new_donor|A new donor Galera node was detected new_ndb|A new MySQL Cluster node was found