Kubernetes - Readiness And Liveness Probes 🛸

Description 👀

At times you may want to check if a container is ready to serve requests. Or you may want to check if a container is alive and healthy. That’s where readinessProbes and livenessProbes come in.

• Readiness Probes

  readinessProbes are used to check if a container is ready to serve requests. If a readinessProbe fails, the container will not receive any traffic from a service. However, if a readinessProbe fails, the container will not be restarted, unless it is also unhealthy.

• Liveness Probes

  livenessProbes are used to check if a container is alive and healthy. If a livenessProbe fails, the container will be restarted. livenessProbes are useful when containers become unresponsive due to memory leaks or deadlocks.

Examples 🧩

• sample readinessProbe definition

    apiVersion: v1
    kind: Pod
    metadata:
        name: readiness-probe
    spec:
        containers:
          - name: readiness-probe
            image: nginx
            readinessProbe:
                httpGet:
                path: /index.html
                port: 80
  
                # for tcp
                # tcpSocket:
                #   port: 80
  
                # for exec
                # exec:
                #   command:
                #     - cat
                #     - /tmp/healthy
  
                initialDelaySeconds: 5
                periodSeconds: 5
  

• sample livenessProbe definition

    apiVersion: v1
    kind: Pod
    metadata:
        name: readiness-probe
    spec:
        containers:
          - name: web-app
            image: web-app
            ports:
              - containerPort: 8080
            livenessProbe:
                httpGet:
                path: /health
                port: 8080
  
                # for tcp
                # tcpSocket:
                #   port: 8080
              
                # for exec
                # exec:
                #   command:
                #     - cat
                #     - /tmp/healthy
                  
                initialDelaySeconds: 5
                periodSeconds: 5
  

• sample pod with readiness and liveness probe

    apiVersion: v1
    kind: Pod
    metadata:
        labels:
            name: simple-webapp
        name: simple-webapp
    spec:
        containers:
        - name: simple-webapp
            image: kodekloud/webapp-delayed-start
            imagePullPolicy: Always
            env:
            - name: APP_START_DELAY
                value: "80"
            ports:
            - containerPort: 8080
            protocol: TCP
            readinessProbe:
                httpGet:
                    path: /ready
                    port: 8080
            livenessProbe:
                httpGet:
                    path: /live
                    port: 8080
                initialDelaySeconds: 80
                periodSeconds: 1
  

↩️