# 05 — StatefulSet: for Pods that are NOT interchangeable. Stable network
# identity (postgres-0, postgres-1...), stable per-Pod storage that
# survives reschedule, and ordered, one-at-a-time rollout.
#
#   kubectl apply -f 05-statefulset.yaml
#   kubectl get pods -l app=postgres        # -0 then -1 then -2, in order
#   kubectl get pvc                         # one PVC per Pod, kept on delete
#   kubectl delete pod postgres-1           # comes back as postgres-1, same disk
#
# The headless Service (clusterIP: None) is what gives each Pod its own
# DNS name: postgres-0.postgres.default.svc.cluster.local
---
apiVersion: v1
kind: Service
metadata:
  name: postgres
  labels:
    app: postgres
spec:
  clusterIP: None
  selector:
    app: postgres
  ports:
    - name: postgres
      port: 5432
      targetPort: postgres
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: postgres
spec:
  serviceName: postgres
  replicas: 3
  podManagementPolicy: OrderedReady
  updateStrategy:
    type: RollingUpdate
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      securityContext:
        runAsNonRoot: true
        runAsUser: 999
        fsGroup: 999
      terminationGracePeriodSeconds: 60
      containers:
        - name: postgres
          image: postgres:16.4-alpine
          ports:
            - containerPort: 5432
              name: postgres
          env:
            - name: POSTGRES_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: api-secrets
                  key: JWT_SIGNING_KEY
            - name: PGDATA
              value: /var/lib/postgresql/data/pgdata
          resources:
            requests:
              cpu: 250m
              memory: 512Mi
            limits:
              cpu: "2"
              memory: 2Gi
          readinessProbe:
            exec:
              command: ["pg_isready", "-U", "postgres"]
            initialDelaySeconds: 10
            periodSeconds: 5
          livenessProbe:
            exec:
              command: ["pg_isready", "-U", "postgres"]
            initialDelaySeconds: 30
            periodSeconds: 10
          volumeMounts:
            - name: data
              mountPath: /var/lib/postgresql/data
          securityContext:
            allowPrivilegeEscalation: false
            capabilities:
              drop: ["ALL"]
  volumeClaimTemplates:
    - metadata:
        name: data
      spec:
        accessModes: ["ReadWriteOnce"]
        storageClassName: fast-ssd
        resources:
          requests:
            storage: 20Gi