[HADOOP-8163] Improve ActiveStandbyElector to provide hooks for fencing old active

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.23.3, 0.24.0
• Fix Version/s: 2.0.0-alpha
• Component/s: ha
• Target Version/s: 0.23.3, 0.24.0
• Hadoop Flags: Reviewed
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 12/Mar/12 23:18
• Updated: 23/May/12 20:15
• Resolved: 24/Mar/12 00:08

Description

When a new node becomes active in an HA setup, it may sometimes have to take fencing actions against the node that was formerly active. This JIRA extends the ActiveStandbyElector which adds an extra non-ephemeral node into the ZK directory, which acts as a second copy of the active node's information. Then, if the active loses its ZK session, the next active to be elected may easily locate the unfenced node to take the appropriate actions.