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 5.2.2, “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.