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https://issues.apache.org/jira/browse/ZOOKEEPER-2554?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15466268#comment-15466268
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Alexander Shraer commented on ZOOKEEPER-2554:
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Non-voting follower is very different from observer. Observers only get inform
(its like commit) messages, while non-voting followers are just like normal
followers - they get propose and commit, and also reply with ACKs to the leader
but the leader silently ignores their votes. They don't count for a quorum
needed to commit an operation. This mode existed before 3.5 - when you connect
any server to the ZK cluster, it just starts working as a follower. I used it
for reconfiguration as the state for servers that are not part of the
configuration. When a new server joins, it will initially become a non-voting
follower, so it is not necessary to start it as observer, you can just as well
start it as participant, because the conversion OBSERVER -> PARTICIPANT is
automatic as you noticed.
So - just start it as participant and issue a reconfig to turn it into an
observer.
> reconfig can not add new server as observer
> -------------------------------------------
>
> Key: ZOOKEEPER-2554
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2554
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.5.0, 3.5.1, 3.5.2
> Reporter: Arshad Mohammad
> Assignee: Arshad Mohammad
> Priority: Critical
> Attachments: ReconfigObserverTest.java, ZOOKEEPER-2554-01.patch
>
>
> Try to add new observer server using reconfig API, server gets added as
> participant.
> STEPS:
> # create 3 node cluster.
> {code}
> server.0=127.0.0.1:11223:11224:participant;127.0.0.1:11222
> server.1=127.0.0.1:11226:11227:participant;127.0.0.1:11225
> server.2=127.0.0.1:11229:11230:participant;127.0.0.1:11228
> {code}
> # Suppose the 2 is the leader in the above cluster. Configure the new server
> as
> {code}
> server.2=127.0.0.1:11229:11230:participant;127.0.0.1:11228
> server.3=127.0.0.1:11232:11233:observer;127.0.0.1:11231
> {code}
> # Connect to 1 and execute the reconfig command
> {code}
> zkClient.reconfig("server.3=127.0.0.1:11232:11233:observer;127.0.0.1:11231",
> null, null, -1, null, null);
> {code}
> # Verify sever 3. It was supposed to run as observer but it is running as
> participant
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