[#MXS-3532] Do not allow Galera master to be set to Drain

When using the Galera Monitor, you are able to update a node to the Drain state when it is the Master server.

I have a 3 node cluster with a Read-Write-Split service. When you update the state of the master server to Maintenance, another server is promoted to master. However, when you update the state of the master server to Drain, that server remains as master and no new connections can be established to that cluster.

name: [mariadb-01] status: [Slave, Synced, Running] state: [IN_USE] last opened at: [Mon May  3 17:13:28 2021] last closed at: [not closed] last close reason: [] num sescmd: [0]

name: [mariadb-02] status: [Draining, Master, Synced, Running] state: [NOT_IN_USE] last opened at: [not opened] last closed at: [not closed] last close reason: [] num sescmd: [0]

name: [mariadb-03] status: [Slave, Synced, Running] state: [IN_USE] last opened at: [Mon May  3 17:13:28 2021] last closed at: [not closed] last close reason: [] num sescmd: [0]

2021-05-03 17:13:42   error  : (17675469) [mariadbclient] Routing the query failed. Session will be closed.

2021-05-03 17:13:42   warning: (17675538) [readwritesplit] (Read-Write-Service) [Read-Write-Service] Write query received from user@::ffff:192.168.1.137. Could not find a valid master connection. Closing client connection.

2021-05-03 17:13:42   error  : (17675538) [readwritesplit] (Read-Write-Service) Could not find valid server for target type TARGET_MASTER (COM_STMT_EXECUTE: ), closing connection.

[MXS-3532] Do not allow Galera master to be set to Drain Created: 2021-05-04 Updated: 2021-08-04 Resolved: 2021-08-04
Status:	Closed
Project:	MariaDB MaxScale
Component/s:	galeramon
Affects Version/s:	2.5.10
Fix Version/s:	2.5.15

[MXS-3532] Do not allow Galera master to be set to Drain Created: 2021-05-04 Updated: 2021-08-04 Resolved: 2021-08-04