StatefulSet ordering and naming in Kubernetes - Mini Project: Build & Apply

StatefulSet Ordering and Naming in Kubernetes

📖 Scenario: You are managing a Kubernetes cluster that runs a database application. You want to deploy multiple instances of this database using a StatefulSet. StatefulSets give each pod a unique name and ensure they start in order, which is important for your database to work correctly.

🎯 Goal: Learn how to create a StatefulSet with 3 replicas, understand how Kubernetes names each pod, and see the order in which pods start.

📋 What You'll Learn

Create a StatefulSet YAML manifest with 3 replicas

Set the container image to nginx:latest

Use a volumeClaimTemplates section for persistent storage

Observe pod names and startup order

💡 Why This Matters

🌍 Real World

StatefulSets are used to deploy applications that need stable network IDs and persistent storage, like databases or clustered services.

💼 Career

Understanding StatefulSets is important for Kubernetes administrators and DevOps engineers managing stateful applications in production.

1

Create a StatefulSet YAML with 3 replicas

Create a YAML file named statefulset.yaml with a StatefulSet resource named web. Set replicas to 3. Use nginx:latest as the container image. Include a volumeClaimTemplates section with a persistent volume claim named www requesting 1Gi storage.

Kubernetes

# Write the StatefulSet YAML manifest here

Need a hint?

Remember to set replicas to 3 and include volumeClaimTemplates with the correct storage size.

2

Add a headless service for the StatefulSet

Add a YAML manifest for a headless Service named nginx with clusterIP: None and selector app: nginx. This service is required for the StatefulSet to manage network identities.

Kubernetes

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

# Add the headless Service YAML below

Need a hint?

The headless service must have clusterIP: None and select pods with label app: nginx.

3

Deploy the StatefulSet and check pod names

Use the command kubectl apply -f statefulset.yaml to deploy the StatefulSet and Service. Then use kubectl get pods -l app=nginx to list the pods. Notice the pod names are web-0, web-1, and web-2.

Kubernetes

apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

# Run the kubectl commands below

Need a hint?

Use kubectl apply -f statefulset.yaml to deploy and kubectl get pods -l app=nginx to see pod names.

4

Observe pod startup order and print pod names

Write a command to print the pod names in order using kubectl get pods -l app=nginx -o custom-columns=NAME:.metadata.name --no-headers. This shows pods named web-0, web-1, and web-2 in startup order.

Kubernetes

apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

# Print pod names in order below

Need a hint?

Use kubectl get pods -l app=nginx -o custom-columns=NAME:.metadata.name --no-headers to list pod names.