| 1 | Production clusters need at least three control-plane hosts and an odd number of etcd members for Raft quorum. Two topologies are common. On the left, stacked: etcd runs on the same host as the apiserver, simpler to operate and cheaper, at the cost of weaker failure isolation — losing one host loses one apiserver and one etcd member at the same time. On the right, the recommended external topology: etcd runs on dedicated hosts in its own tier, so the storage layer can survive apiserver pressure independently. Scheduler and controller-manager are leader-elected in either topology, which is why running three replicas is safe. |