Robert Kamphuis created ZOOKEEPER-2107:
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Summary: zookeeper client should support custom HostProviders
Key: ZOOKEEPER-2107
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2107
Project: ZooKeeper
Issue Type: Improvement
Components: java client
Affects Versions: 3.5.0
Reporter: Robert Kamphuis
Fix For: 3.5.1
The zookeeper client currently contains a StaticHostProvider and no means to
replace it with your own implementation of the existing HostProvider interface.
It would be great if the zookeeper client would enable you to create an
instance with your own implementation of the HostProvider interface.
We have been testing this change with our implementation of HostProvider which
does the name to ip lookup at the time of finding the next() server to connect
to. In our AWS based deployments, this enables that applications can actually
connect to swapped out zookeeper-servers which typically get a new ip address.
With the current StaticHostProvider in practice you will need to restart the
application to see the replaced zookeeper as the application continues to try
to connect to the old no longer existing IP address.
With this little change plus a straightforward implementation of the
HostProvider interface (our LateResolvingHostProvider), we can replace the
zookeeper servers one at a time, re-assigning the elastic ips we use for the
zookeeper servers, and have the application servers re-connect to the zookeeper
cluster including the replaced ones without any downtime and without having to
rely on the elastic ips for client to zookeeper-server connections. The reason
for not using elastic-ips in the connect-strings but use the names which map to
the (changing) private ips is to be able to rely on security-groups to control
access.
While this seems very specific for AWS, this anyway seems a generic improvement
for other deployments where the mapping from server name to IP address is not
static.
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