StatefulSets
A StatefulSet manages stateful applications that require stable identities and persistent storage.
- Pods are created in order (0, 1, 2, ...) and terminated in reverse order
- Each Pod gets a stable hostname:
<statefulset-name>-<ordinal>(e.g.web-0,web-1) - Each Pod can have its own PersistentVolumeClaim that persists across rescheduling
- Requires a Headless Service for network identity
Example
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: web
spec:
serviceName: "web"
replicas: 3
selector:
matchLabels:
app: web
template:
metadata:
labels:
app: web
spec:
containers:
- name: nginx
image: nginx:1.25
volumeMounts:
- name: data
mountPath: /usr/share/nginx/html
volumeClaimTemplates:
- metadata:
name: data
spec:
accessModes: ["ReadWriteOnce"]
resources:
requests:
storage: 1Gi
Use Cases
- Databases (MySQL, PostgreSQL, MongoDB)
- Distributed systems that require stable network identifiers (Kafka, ZooKeeper, etcd)
- Applications that require ordered deployment, scaling, and deletion
StatefulSet vs Deployment
| Feature | StatefulSet | Deployment |
|---|---|---|
| Pod identity | Stable, persistent | Random, interchangeable |
| Storage | Per-Pod PVC (persists) | Shared or ephemeral |
| Ordering | Ordered create/delete | Parallel |
| Network | Stable hostname per Pod | Random hostname |