[jira] [Created] (ZOOKEEPER-1723) unique ensemble identifier

["Mohammad Shamma (JIRA)" <ji...@apache.org>]

Mohammad Shamma created ZOOKEEPER-1723:
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             Summary: unique ensemble identifier
                 Key: ZOOKEEPER-1723
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1723
             Project: ZooKeeper
          Issue Type: Bug
          Components: server
            Reporter: Mohammad Shamma


Zookeeper ensembles need an identifier that would prevent misconfigured zookeeper server from clobbering the configuration of a zookeeper ensemble.

Use case:

- A zookeeper based distributed system that grows its zookeeper ensemble incrementally.
- The system is reset, where the new zookeeper ensemble is a subset of the old zookeeper ensemble (the history of the new ensemble have been reset too).
- The old zookeeper servers will attempt to communicate with the new servers (assuming the network end-points remain the same).
- The new zookeeper servers will notice that the old zookeeper servers have a higher configuration version and will attempt to reconfigure based on the old ensemble configuration info.

Note that this can be solved if the reset process would stop every zookeeper server in the old deployment and delete its history. However, some of these servers might be down at the time of reset, therefore this solution is not reliable.

I am sure this is not the most generic description of the problem of not having ensemble identifiers, but it presents a use case for introducing them to prevent servers from cross-talking across different ensembles. Otherwise they will automatically join in to form a single ensemble.

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