The next version of Zookeeper (3.5) allows for dynamic reconfiguration, so it'll be much easier to reconfigure your cluster online. Hopefully we'll also have self-repairing ZK clusters and you won't have to manage Zookeeper unless things are going seriously wrong (e.g. you only have 2 machines online across your whole cluster).

Here's the bug: https://issues.apache.org/jira/browse/ZOOKEEPER-107

It may have taken 5 years, but this will be fixed.

I love etcd & Zookeeper!