[ZOOKEEPER-1031] Introduce virtual cluster IP and start that cluster IP on the host running ZK leader

• Type: Wish
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 3.3.3
• Fix Version/s: 4.0.0
• Component/s: leaderElection, quorum
• Assignee: Unassigned
• Reporter: Vishal Kher
• Created: 26/Mar/11 02:29
• Updated: 28/May/15 05:36

Description

It would be useful to enable a way to specify a virtual (floating) IP for the ZK cluster (say in zoo.cfg). The ZK leader will start this IP on one of its interfaces. If the leadership changes, the cluster IP will be taken over by the new leader. This IP can be used to identify the ZK leader and send administrative commands/query to the leader. For example,

• a ZK client can get the list of ZK servers in the configuration by sending a request to the server running this IP address. The client just needs to know one IP address. Availability of cluster automatically ensures availability of
  the IP address.
• To reconfigure ZK configuration, a client can send reconfig request to the server on this IP and keep retrying until the request succeeds or fails.

Implementation issues:
1. The old ZK leader that has lost leadership should be able to somehow give up the virtual IP address. Otherwise, it could lead to collisions. One solution is to self reboot. A system property can be used to specify ways to unplumb the cluster IP
2. Cross-platform support.
3. Refreshing ARP caches