StatefulSet Hands-on

Target Audience: Developers who want to deploy stateful applications on Kubernetes Prerequisites: Deployment, Service, PersistentVolume concepts After reading this: You will be able to deploy MySQL with StatefulSet and verify data persistence

TL;DR
Deploy MySQL with StatefulSet
Access individual Pods via Headless Service
Persist data with PersistentVolumeClaim templates
Verify data preservation during scale up/down

Overall Flow#

flowchart LR
    A[Headless Service] --> B[StatefulSet]
    B --> C[mysql-0]
    B --> D[mysql-1]
    B --> E[mysql-2]
    C --> F[PVC-0]
    D --> G[PVC-1]
    E --> H[PVC-2]

Prerequisites#

You will need the following:

Local Kubernetes cluster (Minikube or Kind)
kubectl
At least 2GB available memory

# Check cluster status
kubectl cluster-info

# Create namespace
kubectl create namespace statefulset-lab

StatefulSet vs Deployment#

Use StatefulSet for workloads that require the following properties:

Property	Deployment	StatefulSet
Pod name	Random hash	Ordinal index (0, 1, 2…)
Creation/deletion order	Random	Order guaranteed
Network ID	None	Stable (Headless Service)
Storage	Shareable	Unique PVC per Pod

Lab 1: Create Headless Service#

StatefulSet requires a Headless Service. Set clusterIP: None.

# mysql-headless-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: mysql
  namespace: statefulset-lab
  labels:
    app: mysql
spec:
  clusterIP: None
  selector:
    app: mysql
  ports:
  - port: 3306
    targetPort: 3306

kubectl apply -f mysql-headless-service.yaml

Through the Headless Service, you can access each Pod using the format mysql-0.mysql.statefulset-lab.svc.cluster.local.

Lab 2: Create Secret#

Manage the MySQL root password as a Secret.

# mysql-secret.yaml
apiVersion: v1
kind: Secret
metadata:
  name: mysql-secret
  namespace: statefulset-lab
type: Opaque
stringData:
  MYSQL_ROOT_PASSWORD: rootpassword
  MYSQL_DATABASE: testdb

kubectl apply -f mysql-secret.yaml

Lab 3: Deploy StatefulSet#

Create StatefulSet#

# mysql-statefulset.yaml
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mysql
  namespace: statefulset-lab
spec:
  serviceName: mysql
  replicas: 3
  selector:
    matchLabels:
      app: mysql
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - name: mysql
        image: mysql:8.0
        ports:
        - containerPort: 3306
        envFrom:
        - secretRef:
            name: mysql-secret
        resources:
          requests:
            memory: "256Mi"
            cpu: "250m"
          limits:
            memory: "512Mi"
            cpu: "500m"
        volumeMounts:
        - name: mysql-data
          mountPath: /var/lib/mysql
        readinessProbe:
          exec:
            command:
            - mysqladmin
            - ping
            - -h
            - localhost
          initialDelaySeconds: 30
          periodSeconds: 10
        livenessProbe:
          exec:
            command:
            - mysqladmin
            - ping
            - -h
            - localhost
          initialDelaySeconds: 60
          periodSeconds: 15
  volumeClaimTemplates:
  - metadata:
      name: mysql-data
    spec:
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 1Gi

kubectl apply -f mysql-statefulset.yaml

# Verify Pods are created in order
kubectl get pods -n statefulset-lab -l app=mysql -w

Expected output:

NAME      READY   STATUS    RESTARTS   AGE
mysql-0   1/1     Running   0          60s
mysql-1   1/1     Running   0          45s
mysql-2   1/1     Running   0          30s

Verify PVCs#

# Verify unique PVC created for each Pod
kubectl get pvc -n statefulset-lab

Expected output:

NAME                 STATUS   VOLUME       CAPACITY   ACCESS MODES   AGE
mysql-data-mysql-0   Bound    pv-xxx       1Gi        RWO            2m
mysql-data-mysql-1   Bound    pv-yyy       1Gi        RWO            90s
mysql-data-mysql-2   Bound    pv-zzz       1Gi        RWO            60s

Lab 4: Verify Data Persistence#

Insert Data#

# Connect to mysql-0 and insert data
kubectl exec -n statefulset-lab mysql-0 -it -- mysql -uroot -prootpassword -e "
  USE testdb;
  CREATE TABLE messages (id INT AUTO_INCREMENT PRIMARY KEY, content VARCHAR(255));
  INSERT INTO messages (content) VALUES ('Hello from mysql-0');
  SELECT * FROM messages;
"

Verify Data After Pod Restart#

# Delete Pod (StatefulSet will auto-recreate)
kubectl delete pod mysql-0 -n statefulset-lab

# Wait until Pod is Running again
kubectl wait --for=condition=ready pod/mysql-0 -n statefulset-lab --timeout=120s

# Verify data is preserved
kubectl exec -n statefulset-lab mysql-0 -it -- mysql -uroot -prootpassword -e "
  USE testdb;
  SELECT * FROM messages;
"

You can confirm the data remains intact. This is because the PVC exists independently from the Pod.

Lab 5: Individual Pod DNS Access#

# Access each MySQL instance by DNS from a temporary Pod
kubectl run dns-test -n statefulset-lab --image=busybox:1.36 --rm -it --restart=Never \
  -- nslookup mysql-0.mysql.statefulset-lab.svc.cluster.local

kubectl run dns-test -n statefulset-lab --image=busybox:1.36 --rm -it --restart=Never \
  -- nslookup mysql-1.mysql.statefulset-lab.svc.cluster.local

Lab 6: Scale Up/Down#

Scale Down#

# Scale down from 3 to 2
kubectl scale statefulset mysql -n statefulset-lab --replicas=2

# mysql-2 is deleted first (reverse order)
kubectl get pods -n statefulset-lab -l app=mysql -w

PVC Preservation
PVCs are not deleted when scaling down. When you scale back up, the existing PVC is reconnected.

Verify PVCs#

# mysql-2's PVC still exists
kubectl get pvc -n statefulset-lab

Scale Up#

# Scale back up to 3
kubectl scale statefulset mysql -n statefulset-lab --replicas=3

# mysql-2 reuses its existing PVC
kubectl get pods -n statefulset-lab -l app=mysql -w

Resource Cleanup#

# Delete StatefulSet
kubectl delete statefulset mysql -n statefulset-lab

# PVCs must be deleted manually
kubectl delete pvc -l app=mysql -n statefulset-lab

# Delete Service, Secret
kubectl delete service mysql -n statefulset-lab
kubectl delete secret mysql-secret -n statefulset-lab

# Delete namespace (includes all resources)
kubectl delete namespace statefulset-lab

Next Steps#

After completing the StatefulSet hands-on, proceed to the following:

Goal	Recommended Document
Access control	RBAC Configuration Lab
Periodic tasks	CronJob Lab
Resource management	Resource Management