StatefulSets and Persistent Storage#
Deployments treat pods as interchangeable. StatefulSets do not – each pod gets a stable hostname, a persistent volume, and an ordered startup sequence. This is what you need for databases, message queues, and any workload where identity matters.
StatefulSet vs Deployment#
| Feature | Deployment | StatefulSet |
|---|---|---|
| Pod names | Random suffix (web-api-6d4f8) | Ordinal index (postgres-0, postgres-1) |
| Startup order | All at once | Sequential (0, then 1, then 2) |
| Stable network identity | No | Yes, via headless Service |
| Persistent storage | Shared or none | Per-pod via volumeClaimTemplates |
| Scaling down | Removes random pods | Removes highest ordinal first |
Use StatefulSets when your application needs any of: stable hostnames, ordered deployment/scaling, or per-pod persistent storage. Common examples: PostgreSQL, MySQL, Redis Sentinel, Kafka, ZooKeeper, Elasticsearch.