Coordination Service Stack — Consensus Outsourced (ZooKeeper / etcd / Consul)

Coordination Service Stack — Consensus Outsourced (ZooKeeper / etcd / Consul) An architecture diagram generated by Archify. App node A · holds a lease · App cluster — many nodes App node A holds a lease App node B · sends heartbeats · App cluster — many nodes App node B sends heartbeats App node C · registers endpoint · App cluster — many nodes App node C registers endpoint Coordination service · ZooKeeper / etcd / Consul · small fixed cluster: 3 or 5 nodes · Chubby-style Coordination service ZooKeeper / etcd / Consul Chubby-style Consensus core · Raft / Zab / Paxos · small fixed cluster: 3 or 5 nodes · in-memory + durable log Consensus core Raft / Zab / Paxos in-memory + durable log Locks & leases · only one winner · Architecture component Locks & leases only one winner Fencing tokens · zxid / revision · Architecture component Fencing tokens zxid / revision Failure detection · session + heartbeat · Architecture component · ephemeral nodes Failure detection session + heartbeat ephemeral nodes Change notifications · watch keys, no polling · Architecture component Change notifications watch keys, no polling Leader election · one active leader · Architecture component Leader election one active leader Shard assignment · rebalance on join / fail · Architecture component Shard assignment rebalance on join / fail Config management · watch + reload · Architecture component Config management watch + reload Service discovery · register endpoints · Architecture component · optional / cache-first Service discovery register endpoints optional / cache-first acquire lease heartbeat register replicated log atomic ops log index sessions key changes elect leader token assign watch notify App cluster — many nodes small fixed cluster: 3 or 5 nodes Legend Backend Database Cloud