Kubernetes stores all its state in etcd. Every pod spec, every deployment, every service endpoint. When a pod is scheduled, etcd records it. When a service endpoint changes, etcd records it. Everything that needs to be consistent across all Kubernetes control plane components lives there. etcd is a strongly consistent key-value store built on Raft. Understanding why you’d want this for configuration, and specifically the watch mechanism that makes it useful, is the interesting part.

100 nodes in a cluster. Every node needs to know when another node fails. If every node heartbeats every other node, that’s 9,900 heartbeat streams. At scale, this becomes the majority of your network traffic. How SWIM Works SWIM (Scalable Weakly-consistent Infection-style Membership) uses gossip-based dissemination with indirect probing. Instead of every node monitoring every other node, each node monitors a small random subset. When a node suspects another has failed, it asks a few other nodes to probe the suspect on its behalf.