add static/readonly client session type
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Key: ZOOKEEPER-520
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-520
Project: Zookeeper
Issue Type: New Feature
Components: c client, java client
Reporter: Patrick Hunt
Fix For: 3.3.0
Occasionally people (typically ops) has asked for the ability to start a ZK
client with a hardcoded, local, non cluster based session. Meaning that you can
bring up a particular client with a hardcoded/readonly view of the ZK namespace
even if the zk cluster is not available. This seems useful for a few reasons:
1) unforseen problems - a client might be brought up and partial application
service restored even in the face of catastrophic cluster failure
2) testing - client could be brought up with a hardcoded configuration for
testing purposes. we might even be able to extend this idea over time to allow
"simulated changes" ie - simulate other clients making changes in the
namespace, perhaps simulate changes in the state of the cluster (testing state
change is often hard for users of the client interface)
Seems like this shouldn't be too hard for us to add. The session could be
established with a URI for a local/remote file rather than a URI of the cluster
servers. The client would essentially read this file which would be a simple
representation of the znode namespace.
/foo/bar "abc"
/foo/bar2 "def"
etc...
In the pure client readonly case this is simple. We might also want to allow
writes to the namespace (essentially back this with an in memory hash) for
things like group membership (so that the client continues to function).
Obv this wouldn't work in some cases, but it might work in many and would allow
further options for users wrt building a relable/recoverable service on top of
ZK.
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