[jboss-jira] [JBoss JIRA] Resolved: (JBAS-4229) HASingletonController doesn't handle "split brain" correctly.

HASingletonController doesn't handle "split brain" correctly. ------------------------------------------------------------- Key: JBAS-4229 URL: http://jira.jboss.com/jira/browse/JBAS-4229 Project: JBoss Application Server Issue Type: Bug Security Level: Public(Everyone can see) Components: Clustering Affects Versions: JBossAS-4.0.3 SP1, JBossAS-4.2.0.CR1, JBossAS-4.0.5.GA, JBossAS-4.0.4.GA Reporter: Adrian Brock Assigned To: Brian Stansberry Fix For: JBossAS-4.2.0.GA The HASingletonController doesn't understand the "split brain" problem. Take for example a JBossMQ destination (queue) which needs to be "restored" from the database when a new singleton is elected. The scenario goes as follows: STEP1 (original state): cluster=server1, server2 master=server1 STEP2 (unplug server1 from the network): cluster=server2 master=server2 server2 will now restore the queue from the database BUT! server1 has the view cluster=server1 master=server1 STEP3 (plug server1 back into the network) cluster=server1, server2 master=server1 We are back to the original state, but since server1 thinks it never left the cluster, it doesn't restore the changes (from the database) that server2 made to the queue between STEP2 and STEP3. This is because it doesn't restart the HASingleton on server1. If there was a third server (server3) to abitrate this wouldn't be a problem. Both server2 and server3 would agree that server2 is the master and that server1 has left and must rejoin. There needs to be some extra processing in the "merge" when two masters agree to form a cluster that ensures that whoever they elect as the new master gets its HASingleton(s) restarted. Otherwise, it won't have the up-to-date state from the other master.