Kube-faq

# Deployment-vs-StatefulSet

Taking PostgreSQL as example:

## StatefulSet

```yaml

kind: StatefulSet

apiVersion: apps/v1

metadata:

  name: postgresql

spec:

  replicas: 1

  serviceName: postgresql

  selector:

    matchLabels:

      app: postgresql

  template:

    metadata:

      creationTimestamp: null

      labels:

        app: postgresql

    spec:

      containers:

        - name: postgresql

          image: docker.io/centos/postgresql-12-centos8:latest

          envFrom:

            - secretRef:

                name: database

          ports:

            - name: postgresql

              containerPort: 5432

              protocol: TCP

          resources:

            requests:

              cpu: "200m"

              memory: "128Mi"

            limits:

              cpu: "400m"

              memory: "256Mi"

          readinessProbe:

            tcpSocket:

              port: 5432

            timeoutSeconds: 1

            periodSeconds: 10

            successThreshold: 1

            failureThreshold: 3

          livenessProbe:

            tcpSocket:

              port: 5432

            timeoutSeconds: 1

            periodSeconds: 10

            successThreshold: 1

            failureThreshold: 3

          volumeMounts:

            - name: postgresql

              mountPath: /var/lib/pgsql/data

          terminationMessagePath: /dev/termination-log

          terminationMessagePolicy: File

          imagePullPolicy: Always

      restartPolicy: Always

      terminationGracePeriodSeconds: 10

      dnsPolicy: ClusterFirst

      securityContext: {}

      schedulerName: default-scheduler

  volumeClaimTemplates:

    - metadata:

        name: postgresql

        labels:

          app: postgresql

      spec:

        accessModes:

          - ReadWriteOnce

        storageClassName: changed-by-upper-kustomize

        volumeMode: Filesystem

        resources:

          requests:

            storage: 500Mi

```

## Deployment

Here we have a split. We have to explicit declare the PVC:

```yaml

---

kind: Deployment

apiVersion: apps/v1

metadata:

  name: postgresql

spec:

  replicas: 1

  selector:

    matchLabels:

      app: postgresql

  template:

    metadata:

      labels:

        app: postgresql

    spec:

      containers:

        - name: postgresql

          image: docker.io/centos/postgresql-12-centos8:latest

          envFrom:

            - secretRef:

                name: database

          resources:

            requests:

              cpu: "200m"

              memory: "128Mi"

            limits:

              cpu: "400m"

              memory: "256Mi"

          readinessProbe:

            tcpSocket:

              port: 5432

            timeoutSeconds: 1

            periodSeconds: 10

            successThreshold: 1

            failureThreshold: 3

          livenessProbe:

            tcpSocket:

              port: 5432

            timeoutSeconds: 1

            periodSeconds: 10

            successThreshold: 1

            failureThreshold: 3

          volumeMounts:

            - name: postgresql

              mountPath: /var/lib/pgsql/data

          terminationMessagePath: /dev/termination-log

          terminationMessagePolicy: File

          imagePullPolicy: Always

      restartPolicy: Always

      terminationGracePeriodSeconds: 10

      dnsPolicy: ClusterFirst

      securityContext: {}

      schedulerName: default-scheduler

      volumes:

      - name: postgresql

        persistentVolumeClaim:

          claimName: postgresql

  strategy:

    type: RollingUpdate

    rollingUpdate:

      maxUnavailable: 25%

      maxSurge: 25%

  revisionHistoryLimit: 10

  progressDeadlineSeconds: 600

---

kind: PersistentVolumeClaim

apiVersion: v1

metadata:

  name: postgresql

spec:

  accessModes:

    - ReadWriteOnce

  resources:

    requests:

      storage: 2Gi

  storageClassName: changed-by-upper-kustomize

  volumeMode: Filesystem

```