75.8 Project 38: StatefulSet MySQL with persistent volumes

echo 'StatefulSet gives stable network identity and ordered Pods for databases'

echo 'volumeClaimTemplates create a PVC per Pod automatically'

echo 'Headless Service (clusterIP None) lets Pods resolve mysql-0.mysql'

mkdir -p /tmp/k8s38 && printf '%s\n' 'apiVersion: v1' 'kind: Service' 'metadata: {name: mysql}' 'spec:' '  clusterIP: None' '  selector: {app: mysql}' '  ports: [{port: 3306, name: mysql}]' > /tmp/k8s38/svc.yaml && grep clusterIP /tmp/k8s38/svc.yaml

kubectl apply -f /tmp/k8s38/svc.yaml

kubectl get svc mysql -o jsonpath='{.spec.clusterIP}'; echo

printf '%s\n' 'apiVersion: apps/v1' 'kind: StatefulSet' 'metadata: {name: mysql}' 'spec:' '  serviceName: mysql' '  replicas: 1' '  selector: {matchLabels: {app: mysql}}' '  template:' '    metadata: {labels: {app: mysql}}' '    spec:' '      containers:' '      - name: mysql' '        image: mysql:8.0' '        env:' '        - {name: MYSQL_ALLOW_EMPTY_PASSWORD, value: "yes"}' '        - {name: MYSQL_DATABASE, value: shop}' '        ports: [{containerPort: 3306, name: mysql}]' '        volumeMounts: [{name: data, mountPath: /var/lib/mysql}]' '  volumeClaimTemplates:' '  - metadata: {name: data}' '    spec:' '      accessModes: [ReadWriteOnce]' '      resources: {requests: {storage: 1Gi}}' > /tmp/k8s38/sts.yaml && grep volumeClaimTemplates /tmp/k8s38/sts.yaml

kubectl apply -f /tmp/k8s38/sts.yaml

kubectl rollout status statefulset/mysql --timeout=180s

kubectl get pods -l app=mysql -o wide

kubectl get pvc

kubectl get sts mysql

kubectl exec mysql-0 -- mysql -e 'SHOW DATABASES;'

kubectl exec mysql-0 -- mysql -e 'CREATE TABLE shop.items(id INT PRIMARY KEY, name VARCHAR(20)); INSERT INTO shop.items VALUES (1,"pen"); SELECT * FROM shop.items;'

echo 'Lab uses empty password only on kind; never in real clusters'

kubectl delete pod mysql-0

kubectl rollout status statefulset/mysql --timeout=180s

kubectl exec mysql-0 -- mysql -N -e 'SELECT name FROM shop.items WHERE id=1;'

kubectl get pv | head -5

kubectl get sc

echo 'Production picks gp3 or similar; set storageClassName explicitly'

echo 'Ordinals: mysql-0 then mysql-1 when replicas grow'

echo 'Do not scale MySQL StatefulSet like a stateless web app without a plan'

echo 'Operators like Percona charts handle HA better than raw STS alone'

kubectl get endpoints mysql

echo 'DNS shape for ordinal 0 is mysql-0.mysql.default.svc.cluster.local'

echo 'Use nslookup from a busybox Pod to prove it on your lab'

kubectl describe pvc data-mysql-0 | head -15

kubectl get sts mysql -o jsonpath='{.spec.serviceName}'; echo

echo 'Default delete of STS removes Pods; PVCs often remain until you delete them'

echo 'Backup tip: use mysqldump to an object store on a schedule'

echo 'Snapshot tip: VolumeSnapshots for faster restore drills'

echo 'Fix data dir ownership with securityContext runAsUser; never world-writable modes'

kubectl get pods -l app=mysql --no-headers | awk '{print $1,$3}'

kubectl exec mysql-0 -- mysql -N -e 'SELECT COUNT(*) FROM shop.items;'

echo 'Imran: PASS'