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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
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