To monitor the status of each guarded server instance, the MySQL Instance Manager attempts to connect to the instance at regular intervals using the MySQL_Instance_Manager@localhost user account with a password of check_connection.

You are not required to create this account for MySQL Server; in fact, it is expected that it will not exist. Instance Manager can tell that a server is operational if the server accepts the connection attempt but refuses access for the account by returning a login error. However, these failed connection attempts are logged by the server to its general query log (see Section 5.11.3, “The General Query Log”).

Instance Manager also attempts a connection to nonguarded server instances when you use the SHOW INSTANCES or SHOW INSTANCE STATUS command. This is the only status monitoring done for nonguarded instances.

Instance Manager knows if a server instance fails at startup because it receives a status from the attempt. For an instance that starts but later crashes, Instance Manager receives a signal because it is the parent process of the instance.

Beginning with MySQL 5.1.12, Instance Manager tracks instance states so that it can determine which commands are allowed for each instance. For example, commands that modify an instance's configuration are allowed only while the instance is offline.

Each instance is in one of the states described in the following table. Guarded instances can be in any of the states. Nonguarded instances can only be offline or online. Instance state information is displayed in the status column of the SHOW INSTANCES and SHOW INSTANCE STATUS commands.