Patrick Hunt updated ZOOKEEPER-641:
Fix Version/s: (was: 3.3.0)
> Improve details about group membership recipe
> Key: ZOOKEEPER-641
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-641
> Project: Zookeeper
> Issue Type: Improvement
> Components: documentation
> Affects Versions: 3.2.1
> Reporter: Adam Rosien
> Fix For: 3.4.0
> Patrick Hunt asked for a more complete group membership recipe from the one
> listed at
> The relevant text from the blog post:
> One type of group management system using ZooKeeper:
> * A group contains some logical service. The *meaning* of belonging to a
> group is typically "the instance is available for use by clients over the
> * Services can join and leave the group. The special case of a service
> crashing or a network outage needs to be handled as leaving the group.
> * Joined services share metadata about how to communicate with it, i.e.,
> its IP address, base URL, etc.
> * Clients can ask what instances are in the group, i.e., available.
> * Clients are notified when group membership changes so they can mutate
> their local state.
> These map onto ZooKeeper as:
> * A group is a (permanent) node in the ZooKeeper hierarchy. Clients and
> services must be told the path to this node.
> * A services joins the group by creating an ephemeral node whose parent
> is the group node. By using an ephemeral node, if the service dies then the
> service is automatically removed from the group.
> * The ephemeral node's data contains the service metadata in some format
> like JSON, XML, Avro, Protobufs, Thrift, etc. ZooKeeper has no equivalent of
> HTTP's "Content-Type" header to identify the metadata representation, so
> services and clients must agree upon the format in some manner.
> * Clients can query for the children of the group node to identify the
> members of the group.
> * Clients can place a watch on the group node to be notified if nodes
> have joined or left the group.
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