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From "Benjamin Reed (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-107) Allow dynamic changes to server cluster membership
Date Mon, 04 May 2009 22:32:30 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12705794#action_12705794

Benjamin Reed commented on ZOOKEEPER-107:

sounds great henry! it would be great if you could work on this.

i think we have two strategies:

1) have the cluster agree on a list of servers and use the atomic broadcast to agree on changes.
(this might be a bit more difficult with the flexible quorum configuration. right flavio?)
this is mostly in line with your first three points. btw, i don't think you need to quiesce
for this or even do the sync. i think you can do a conditional update.

2) use some external resource file indicated by a URL to define the machines that make up
a cluster. this is in line with your last point and you hint at this with your first point.

i think the first approach is safer and more reliable. the second is easier to implement and
easier to see what is going on, but i during transition time you have a problem as the resource
file propagates through the cluster. (you could have different members with different views.)

the thing i was thinking of for the first option is exposing the cluster config through a
znode '/.zookeeper/ensemble' or something like that. then changing the configuration would
be as "simple" as conditionally setting a new version of that file. the tricky part is that
you could only commit the change if you have a quorum of followers in both the old and the
new configuration. this seems to be in line with what you are thinking correct?

> Allow dynamic changes to server cluster membership
> --------------------------------------------------
>                 Key: ZOOKEEPER-107
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-107
>             Project: Zookeeper
>          Issue Type: Improvement
>          Components: server
>            Reporter: Patrick Hunt
> Currently cluster membership is statically defined, adding/removing hosts to/from the
server cluster dynamically needs to be supported.

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