Andraz Tori commented on ZOOKEEPER-107:

Has anything happened with this feature?

There was some talk about what the most important use cases are on the mailing 
list. We're thinking of migrating home-grown solution to Zookeeper, but can't 
do it without dynamic addition/removal of the servers. If it helps, here's the 
use case:

We're having fully cloudy solution. Every server that we put into the cluster 
runs a set of services that make themselves available to a local "resource 
manager" that shares the list of resources with all other servers in the 
cluster. When we do upgrades we simply fire up new servers with new versions of 
the services and connect their resource managers to the old ones into the same 
cluster. Then we simply shut down the old servers. Beside adding/removing 
servers when upgrading, we also do the same thing when we need to temporarily 
scale - we fire up a few more servers and connect their resource managers to 
the cluster to make the services available to the cluster. 
We never know how many servers there are going to be in the cluster and we 
don't assign any dns entries to them (just another point of failure).
The clients that need to know about resources connect to any of the "resource 
managers" and get a list of all resources available and also about other 
"resource managers". As servers move around they also can connect to different 
"resource manager".

This is a bit unusual configuration since cloud practically lives on its own 
without any kind of static addresses. As long as you are able to connect to it 
at one point in time, you can keep up with it 'motion'. 

So the idea was to migrate the above system to Zookeeper. Every service would 
connect to local Zookeeper and create ephemeral node announcing it. So every 
server would run its own Zookeeper node connected to the Zookeeper cloud. 
However without dynamic addition/removal of the servers all this becomes 

Ideally we'd like to have a situation where we just start a Zookeeper node by 
giving it a list of known other Zookeeper nodes in the cloud. And then it 
should take on to the life of its own.

Hope that the use case helps. I am really looking forward to this!

> 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
>            Assignee: Henry Robinson
>         Attachments: SimpleAddition.rtf
> Currently cluster membership is statically defined, adding/removing hosts 
> to/from the server cluster dynamically needs to be supported.

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