Database with StatefulSet

Write the database as a StatefulSet.

The database with a StatefulSet

The database moves to a single-replica StatefulSet: it gets a stable name (db-0), a persistent disk (data-db-0) and a headless service. The template takes the disk size from the values:

# templates/db-statefulset.yaml (summary)
spec:
  serviceName: db
  replicas: 1
  template:
    spec:
      containers:
        - name: postgres
          image: postgres:16
          envFrom:
            - secretRef: {name: db-gizli}
          volumeMounts:
            - name: data
              mountPath: /var/lib/postgresql/data
  volumeClaimTemplates:
    - metadata: {name: data}
      spec:
        accessModes: ["ReadWriteOnce"]
        resources:
          requests:
            storage: {{ .Values.db.storage }}

Testing the database

After installing, it's tested that the database is ready, the disk is attached and the stable name resolves:

kubectl rollout status sts/db -n magaza
kubectl get pvc -n magaza
kubectl exec -n magaza db-0 -- pg_isready -U postgres
/var/run/postgresql:5432 - accepting connections
kubectl exec -n magaza deploy/api -- getent hosts db-0.db

Exercise Verify the database

Write three commands: wait for sts/db's rollout to finish in magaza; list the PVCs in magaza; run pg_isready -U postgres in the db-0 pod in magaza.

Show example solution

kubectl rollout status sts/db -n magaza
kubectl get pvc -n magaza
kubectl exec -n magaza db-0 -- pg_isready -U postgres

Test yourself

In this setup, what happens to the database data if helm uninstall magaza is run?
- It moves to another namespace
- The PVC (data-db-0) remains; the data is kept
- It's deleted immediately
- It moves to a backup
Show answer

The PVC (data-db-0) remains; the data is kept — PVCs created from volumeClaimTemplates aren't part of the Helm release.

Take the disk size from the values.

            storage: {{ .____.db.storage }}

Show answer

            storage: {{ .Values.db.storage }}

Match.

db-0

Stable pod name
data-db-0

Persistent disk
pg_isready

Is the database ready
db-0.db

Pod DNS name

Next lesson: Ingress and TLS

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