Kubernetes Deployments vs StatefulSets

Choosing between a Deployment and a StatefulSet in Kubernetes can shape how your application runs, scales, and recovers from failure. Both are controllers for managing pods, but they serve different use cases. In this guide, you'll learn the key differences, see real-world examples, and get advice on when to use each.

Prerequisites

You'll need:

• A basic understanding of Kubernetes concepts (pods, services, controllers)
• Access to a Kubernetes cluster for hands-on testing (optional)

What is a Deployment?

A Deployment manages stateless applications. It ensures that a specified number of pod replicas are running at all times. Deployments are ideal for workloads where each pod is interchangeable, such as web servers or API backends.

Key features:

• Pods are identical and interchangeable
• Supports rolling updates and rollbacks
• Easy to scale up or down
• No stable network identity or persistent storage by default

Example:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
        - name: web
          image: nginx:1.25

What is a StatefulSet?

A StatefulSet manages stateful applications that need stable network identities and persistent storage. Each pod in a StatefulSet gets a unique, stable name and can have its own persistent volume.

Key features:

• Each pod has a unique, stable identity (e.g., app-0, app-1)
• Supports ordered, graceful deployment and scaling
• Each pod can have its own persistent storage
• Useful for databases, queues, and clustered applications

Example:

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: db-statefulset
spec:
  serviceName: 'db'
  replicas: 3
  selector:
    matchLabels:
      app: db
  template:
    metadata:
      labels:
        app: db
    spec:
      containers:
        - name: db
          image: postgres:16
          volumeMounts:
            - name: db-data
              mountPath: /var/lib/postgresql/data
  volumeClaimTemplates:
    - metadata:
        name: db-data
      spec:
        accessModes: ['ReadWriteOnce']
        resources:
          requests:
            storage: 10Gi

Key Differences at a Glance

• Identity: Deployments create interchangeable pods; StatefulSets assign each pod a unique, stable identity.
• Storage: Deployments use ephemeral storage by default; StatefulSets can attach persistent volumes to each pod.
• Scaling: Deployments scale pods in any order; StatefulSets scale pods in a defined, ordered sequence.
• Use Case: Use Deployments for stateless apps; use StatefulSets for stateful apps like databases or clustered services.

Overview of the differences

When you scale a Deployment, pods are created or destroyed in any order:

[web-abc123]   [web-def456]   [web-ghi789]

With a StatefulSet, each pod has a stable name and order:

[db-0]   [db-1]   [db-2]

When to Use Each

• Use a Deployment for web servers, stateless APIs, and background workers.
• Use a StatefulSet for databases (PostgreSQL, MongoDB), distributed caches, or any app that needs stable storage and identity.

Next Steps

Try deploying both a Deployment and a StatefulSet in your cluster to see the differences in action. Explore how rolling updates, scaling, and pod restarts behave for each controller.

As your workloads grow, understanding these patterns will help you design more reliable and maintainable systems.