[cogman10]

Not much they have pretty compatible feature overlap. Zookeeper pushes pretty heavily on a smart client rather than handling a lot of stuff server side. If I were to pick I'd go with etcd in a heartbeat. Every con they list on their comparison website is stuff I've personally dealt with in ZK.

https://etcd.io/docs/v3.3/learning/why/#zookeeper

[kbumsik]

Actually I was asking the question looking at the etcd doc you linked. The etcd doc explains like it is just better than Zookeeper.

Then why there are so many projects still rely on Zookeeper and spend so much time on re-writing its features instead of switching to etcd like what OP, ClickHouse (in the discussion), and Kafka (KRaft) are doing? It there something that etcd won't fit?

[hodgesrm]

ClickHouse chose an API compatible rewrite because it allowed the project to banish issues like Zookeeper transaction ID rollover and eliminate an external dependency while allowing a gentle migration to the new "ClickHouse Keeper" implemention. Existing prod deployments of ClickHouse are mostly still on Zookeeper, though new deployments are beginning to use ClickHouse Keeper from the start.

There's a good talk by ClickHouse committer Alexander Sapin that explains the design considerations: https://www.youtube.com/watch?v=abhcCRW09Ac

[dikei]

Very few new projects use Zookeeper now. For older projects, most of them have no issue using Zookeeper, so it's simply not worth the time to rewrite them for etcd.