Coordination as a Managed Dependency

1. Four Primitives, Not Three Products

etcd, ZooKeeper and Consul are usually presented as a choice between products. For design purposes they are close to interchangeable, and the differences that matter are operational rather than architectural.

etcd and Consul use Raft. ZooKeeper uses its own protocol, ZAB, which predates Raft and reaches the same place by a different route. None of that changes how you design against them, because all three expose the same four primitives and everything else is built from those four.

• **A consistent key-value store