20.14.8. About High-availability (HA) Failover
High-availability failover is available with either automatic client failover, or application-level failover, through a live-backup structure. Each live server has a backup server. Only one backup per live server is supported.
The backup server only takes over if the live server crashes and there is a failover. After the live server has been restarted, and if the
allow-failback attribute is set to true, it becomes the live server again. When the original live server takes over, the backup server reverts to being backup for the live server.
Important
Clustering should be enabled even if you are not using the clustering capabilities. This is because each node of the HA cluster must have a cluster-connection to all of the other nodes, in order to negotiate roles with the other servers.
High availability cluster topology is achieved by the live and backup server as they send information about their connection details using IP multicasts. If IP multicasts can not be used, it is also possible to use a static configuration of the initial connections. After the initial connection, the client is informed about the topology. If the current connection is stale, the client establishes a new connection to another node.
After a live server has failed and a backup server has taken over, you will need to restart the live server and have clients fail back. To do this, restart the original live server and kill the new live server. You can do this by killing the process itself or wait for the server to crash on its own. You can also cause failover to occur on normal server shutdown, to enable this set the
failover-on-shutdown property to true in the standalone.xml configuration file:
<failover-on-shutdown>true</failover-on-shutdown>
By default, the
failover-on-shutdown property is set to false.
You can also force the new live server to shutdown when the old live server comes back up allowing the original live server to take over automatically by setting the
allow-failback property to true in the standalone.xml configuration file:
<allow-failback>true</allow-failback>
In replication HA mode, to force the new live server to shutdown when the old live server comes back, set the
check-for-live-server property to true in standalone.xml configuration file:
<check-for-live-server>true</check-for-live-server>