Apache ZooKeeper
ZooKeeper et al. provide only a primitive K/V store and require that application developers build their own system to provide service discovery.
ZooKeeper is Coordinator Service.
ZooKeeper 使用在Kafaka中作为service coordinator. 其也可以用作分布式锁(distributed lock)。
Consul
Consul is based on Riak, which use Gossip Protocl.