Liveness Probes

While

Readiness Probes check the application running inside the container for readiness, Liveness Probes check the application running inside the container periodically to check if the application is healthy (live). If the application becomes unhealthy, the pod gets restarted.

Without liveness probes, the application could be stuck in an infinite loop or frozen while the status of the pod is running, making us believe that the application is working fine. In this case, the pod will not be restarted.

💡

Liveness probes are configured just like Readiness probes, we just use livenessProbe instead of readinessProbe in the pod definition.

HTTP based Liveness Check

This is commonly used for containers hosting web applications. The application exposes an HTTP health check endpoint. Only if the endpoint returns a 200 status code, the container will be considered live.


apiVersion: v1
kind: Pod
metadata:
  labels:
    name: frontend
spec:
  containers:
	  - name: webapp
	    image: webapp
			ports:
				- containerPort: 8080
			livenessProbe:
				httpGet:
					path: /api/ready
					port: 8080

TCP based Liveness Check

This is commonly used for containers hosting databases. The container’s TCP port on which the DB is exposed is checked for liveness.


apiVersion: v1
kind: Pod
metadata:
  labels:
    name: database
spec:
  containers:
	  - name: database
	    image: database
			ports:
				- containerPort: 3306
			livenessProbe:
				tcpSocket:
					port: 3306

Shell Script based Liveness Check

Run a shell script inside the container to check the liveness of the application. The return code of the shell script is used to determine the liveness of the container.


apiVersion: v1
kind: Pod
metadata:
  labels:
    name: app
spec:
  containers:
	  - name: app
	    image: app
			livenessProbe:
				exec:
					command: 
						- cat
						- /app/ready

Configuration


livenessProbe:
	httpGet:
		path: /api/ready
		port: 8080

	initialDelaySeconds: 10
	periodSeconds: 5
	failureThreshold: 5

initialDelaySeconds - start checking for liveness after some delay

periodSeconds - liveness check interval

failureThreshold - how many times to check for liveness before declaring the status of container to failed and restart the container (default 3)