How to check Containers health inside a kubernetes pod using livenessProbe?

A Probe is a diagnostic performed periodically by the kubelet on a Container. To perform a diagnostic, the kubelet calls a Handler implemented by the Container. There are three types of handlers:

  • ExecAction: Executes a specified command inside the Container. The diagnostic is considered successful if the command exits with a status code of 0.
  • TCPSocketAction: Performs a TCP check against the Container’s IP address on a specified port. The diagnostic is considered successful if the port is open.
  • HTTPGetAction: Performs an HTTP Get request against the Container’s IP address on a specified port and path. The diagnostic is considered successful if the response has a status code greater than or equal to 200 and less than 400.

Each probe has one of three results:

  • Success: The Container passed the diagnostic.
  • Failure: The Container failed the diagnostic.
  • Unknown: The diagnostic failed, so no action should be taken.

The kubelet can perform and react to two kinds of probes on running Containers:

  • livenessProbe: Indicates whether the Container is running. If the liveness probe fails, the kubelet kills the Container, and the Container is subjected to its restart policy. If a Container does not provide a liveness probe, the default state is Success.
  • readinessProbe: Indicates whether the Container is ready to service requests. If the readiness probe fails, the endpoints controller removes the Pod’s IP address from the endpoints of all Services that match the Pod. The default state of readiness before the initial delay is Failure. If a Container does not provide a readiness probe, the default state is Success.

In this excercise, I would like to discuss on livenessProbe.

Here is the example for livenessProbe using ExecAction

apiVersion: v1
kind: Pod
metadata:
  labels:
    test: liveness
  name: liveness-exec
spec:
  containers:
  - args:
    - /bin/sh
    - -c
    - echo ok > /tmp/health; sleep 10; rm -rf /tmp/health; sleep 600
    image: gcr.io/google_containers/busybox
    livenessProbe:
      exec:
        command:
        - cat
        - /tmp/health
      initialDelaySeconds: 15
      timeoutSeconds: 1
    name: liveness

Here is the example for livenessProbe using TCPSocketAction

apiVersion: v1
kind: Service
metadata:
  name: wordpress-mysql
  labels:
    app: wordpress
spec:
  ports:
    - port: 3306
  selector:
    app: wordpress
    tier: mysql
  clusterIP: None
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysql-pv-claim
  labels:
    app: wordpress
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
---
apiVersion: apps/v1 # for k8s versions before 1.9.0 use apps/v1beta2  and before 1.8.0 use extensions/v1beta1
kind: Deployment
metadata:
  name: wordpress-mysql
  labels:
    app: wordpress
spec:
  selector:
    matchLabels:
      app: wordpress
      tier: mysql
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: wordpress
        tier: mysql
    spec:
      containers:
      - image: mysql:5.6
        name: mysql
        env:
        - name: MYSQL_ROOT_PASSWORD
          valueFrom:
            secretKeyRef:
              name: mysql-pass
              key: password
        livenessProbe:
          tcpSocket:
            port: 3306
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pv-claim

Here is the example for livenessProbe using HTTPGetAction

apiVersion: v1
kind: Service
metadata:
  name: nginxsvc
  labels:
    app: nginx
spec:
  type: NodePort
  ports:
  - port: 80
    protocol: TCP
    name: http
  - port: 443
    protocol: TCP
    name: https
  selector:
    app: nginx
---
apiVersion: v1
kind: ReplicationController
metadata:
  name: my-nginx
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx
    spec:
      volumes:
      - name: secret-volume
        secret:
          secretName: nginxsecret
      - name: configmap-volume
        configMap:
          name: nginxconfigmap
      containers:
      - name: nginxhttps
        image: ymqytw/nginxhttps:1.5
        command: ["/home/auto-reload-nginx.sh"]
        ports:
        - containerPort: 443
        - containerPort: 80
        livenessProbe:
          httpGet:
            path: /index.html
            port: 80
          initialDelaySeconds: 30
          timeoutSeconds: 1
        volumeMounts:
        - mountPath: /etc/nginx/ssl
          name: secret-volume
        - mountPath: /etc/nginx/conf.d
          name: configmap-volume