Patrick Hunt updated ZOOKEEPER-641:

    Fix Version/s: 3.3.0

Thanks for the feedback, any interest to update the recipe doc and submit a 

forrest can be difficult to wrangle but i'd be happy to help you. If you 
checkout the zk trunk
from apache svn the source file for the recipe docs is:

> 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: 3.3.0
> Regarding 
> http://eng.kaching.com/2010/01/actually-implementing-group-management.html 
> Patrick Hunt asked for a more complete group membership recipe from the one 
> listed at 
> http://hadoop.apache.org/zookeeper/docs/r3.0.0/recipes.html#sc_outOfTheBox.
> 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 
> network".
>     * 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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