Keycloak cluster nodes are allowed to boot concurrenty. When Keycloak server instance boots up it may do some database migration, importing, or first time initializations. A DB lock is used to prevent start actions from conflicting with one another when cluster nodes boot up concurrently.

By default, the maximum timeout for this lock is 900 seconds. If a node is waiting on this lock for more than the timeout it will fail to boot. Typically you won’t need to increase/decrease the default value, but just in case it’s possible to configure it in standalone.xml, standalone-ha.xml, or domain.xml file in your distribution. The location of this file depends on your operating mode.