[maplebed]

I chose Zookeeper to achieve this same goal a while ago (before I heard of etcd). I have been pleasantly surprised at how useful having a coordination service is in my infrastructure in addition to a configuration management service. Because of this, even though etcd looks like it serves distributed configuration management better (aka simpler), I'm happy with my choice of Zookeeper.

Two examples of how a coordination service has been useful:

* cluster wide throttles to help protect overwhelmable backends

* redundancy in maintenance cronjobs that really only want to be run once per cluster per time period

(edited for formatting)

[SEJeff]

How do you power cron from ZK? Do you use something like airbnb's chronos[1]?

[1] http://nerds.airbnb.com/introducing-chronos

[maplebed]

No, I took a different approach. Any normal cron job that wants to be run only once (per cluster) grabs a zookeeper lock. Those that fail to acquire the lock exit and try again during the next interval. This is implemented with a wrapper around the cron job that takes care of locking: https://github.com/ParsePlatform/Ops/blob/master/tools/get_z.... More details here: http://blog.parse.com/2013/03/11/implementing-failover-for-r...