A few reasons we didn't use ZK at the time (some of these are out of date). Zookeeper had: - No TLS security story - An abandoned RPC/serialization system tha

A few reasons we didn't use ZK at the time (some of these are out of date). Zookeeper had: - No TLS security story - An abandoned RPC/serialization system that was hard to use in other languages - A consensus algorithm that differed from systems described in literature - A large RAM footprint Awhile ago some etcd engineers made an experiment in fact to try and run ZK client protocol on etcd with a proxy: https://github.com/etcd-io/zetcd https://github.com/etcd-io/zetcd https://coreos.com/blog/introducing-zetcd https://coreos.com/blog/introducing-zetcd Today, etcd performs much better than ZK and I believe it is much more widely deployed with a wider set of engaged users. https://coreos.com/blog/performance-of-etcd.html https://coreos.com/blog/performance-of-etcd.html