Challenge - StatefulSet

Write a StatefulSet with a volumeClaimTemplate.

Challenge: a three-node cluster

You'll run Redis as a three-replica StatefulSet: each replica will have its own disk and stable DNS name; the replicas will start in parallel (they don't need to wait for each other). Then you'll test the identity and persistence: when a pod is deleted, it should come back with the same name and the same data.

redis-0.redis   redis-1.redis   redis-2.redis
data-redis-0    data-redis-1    data-redis-2

Exercise The StatefulSet

Write a StatefulSet YAML: name redis, serviceName: redis, replicas: 3, podManagementPolicy: Parallel; selector and template label app: redis; container named redis, image redis:7, mounts data at /data; a template named data in volumeClaimTemplates, ReadWriteOnce, 1Gi.

Show example solution

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: redis
spec:
  serviceName: redis
  replicas: 3
  podManagementPolicy: Parallel
  selector:
    matchLabels:
      app: redis
  template:
    metadata:
      labels:
        app: redis
    spec:
      containers:
        - name: redis
          image: redis:7
          volumeMounts:
            - name: data
              mountPath: /data
  volumeClaimTemplates:
    - metadata:
        name: data
      spec:
        accessModes: ["ReadWriteOnce"]
        resources:
          requests:
            storage: 1Gi

Exercise Test persistence

Write four commands: run redis-cli set anahtar deger in redis-1; delete the redis-1 pod; list the pods labelled app=redis; run redis-cli get anahtar in redis-1.

Show example solution

kubectl exec redis-1 -- redis-cli set anahtar deger
kubectl delete pod redis-1
kubectl get pods -l app=redis
kubectl exec redis-1 -- redis-cli get anahtar

Test yourself

What is the benefit of choosing podManagementPolicy: Parallel in this scenario?
- The disks merge
- DNS turns off
- All three pods start at once without waiting; startup is faster
- Data is shared
Show answer

All three pods start at once without waiting; startup is faster — Stable identities and disks are still kept; only the ordering isn't waited for.

Start the pods in parallel.

spec:
  serviceName: redis
  podManagementPolicy: ____

Show answer

spec:
  serviceName: redis
  podManagementPolicy: Parallel

Match.

redis-0

Stable name
data-redis-0

Persistent disk
redis-0.redis

DNS name
Parallel

Start at once

Next lesson: Challenge - CronJob

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