Kubernetes - liveness and Readiness

 Liveness Probe

Many applications running for long periods of time eventually transition to broken states, and cannot recover except by being restarted. Kubernetes provides liveness probes to detect and remedy such situations.

In this exercise, you create a Pod that runs a container based on the k8s.gcr.io/busybox image. Here is the configuration file for the Pod:

apiVersion: v1

kind: Pod

metadata:

  name: myapp

  labels:

    name: myapp

spec:

  containers:

  - name: myapp

    image: k8s.gcr.io/busybox

    args:

      - /bin/sh

      - -c

      - touch /tmp/healthy; sleep 20; rm -f /tmp/healthy; sleep 600

    livenessProbe:

      exec:

        command:

        - cat

        - /tmp/healthy

      initialDelaySeconds: 5

      periodSeconds: 3    

 

Define a liveness HTTP request

Another kind of liveness probe uses an HTTP GET request. Here is the configuration file for a Pod that runs a container based on the k8s.gcr.io/liveness image.

apiVersion: v1

kind: Pod

metadata:

  name: myapp

  labels:

    name: myapp

spec:

  containers:

  - name: myapp

    image: k8s.gcr.io/liveness

    args:

      - /server

    livenessProbe:

      httpGet:

        path: /healthz

        port: 8080

        httpHeaders:

        - name: Custom-Header

          value: Awesome

      initialDelaySeconds: 5

      periodSeconds: 5    

Define a TCP liveness probe

A third type of liveness probe uses a TCP socket. With this configuration, the kubelet will attempt to open a socket to your container on the specified port. If it can establish a connection, the container is considered healthy, if it can't it is considered a failure.

apiVersion: v1

kind: Pod

metadata:

  name: myapp

  labels:

    name: myapp

spec:

  containers:

  - name: myapp

    image: k8s.gcr.io/goproxy:0.1

    ports:

      - containerPort: 8080

    readinessProbe:

      tcpSocket:

        port: 8080

      initialDelaySeconds: 5

      periodSeconds: 10

    livenessProbe:

     tcpSocket:

        port: 8080

     initialDelaySeconds: 15

     periodSeconds: 20

#Example of Readiness

apiVersion: apps/v1

kind: Deployment

metadata:

  creationTimestamp: null

  labels:

    app: podrediness

  name: podrediness

spec:

  replicas: 1

  selector:

    matchLabels:

      app: podrediness

  strategy: {}

  template:

    metadata:

      labels:

        app: podrediness

    spec:

      containers:

      - image: busybox

        name: busybox

        args:

         - /bin/sh

         - -c

         - sleep 20; touch webapp; sleep 600

        readinessProbe:

         exec:

          command:

            - cat

            - webapp

         initialDelaySeconds: 15

         periodSeconds: 3