Skip to main content

StatefulSets: For Databases

Key Takeaways for AI & Readers
  • Identity: Assigns a sticky, unique network ID (e.g., web-0) to each Pod.
  • Persistence: Each Pod maintains its own PersistentVolume across restarts.
  • Ordering: Starts and stops Pods in a predictable, sequential order.
Current: 0 Replicas
Click "Scale Up" to see how pods are created.
Deployments create interchangeable pods with random names. Order doesn't matter.

A StatefulSet manages the deployment and scaling of a set of Pods, providing guarantees about the ordering and uniqueness of these Pods.

Unlike a Deployment, a StatefulSet maintains a sticky identity for each of its Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.

Use Cases​

StatefulSets are valuable for applications that require one or more of the following:

  • Stable, unique network identifiers. (e.g., mysql-0, mysql-1)
  • Stable, persistent storage. (e.g., specific PVCs linked to specific Pods)
  • Ordered, graceful deployment and scaling.
  • Ordered, automated rolling updates.

Examples:

  • Databases (PostgreSQL, MySQL, MongoDB)
  • Distributed systems (Zookeeper, Kafka, Elasticsearch)

Key Features​

1. Stable Network ID​

Pods in a StatefulSet get a predictable name: $(statefulset-name)-$(ordinal). If you define a StatefulSet named web with 3 replicas, you get:

  • web-0
  • web-1
  • web-2

2. Stable Storage​

Kubernetes creates a PersistentVolumeClaim (PVC) for each Pod based on a volumeClaimTemplate. If web-0 dies and is rescheduled on a different node, it re-attaches to the same storage volume it had before.

3. Ordered Deployment​

  • Scale Up: 0 -> 1 -> 2 (Sequential)
  • Scale Down: 2 -> 1 -> 0 (Reverse Sequential)