Exercise 5: Health checks

In Kubernetes, liveness and readiness probes are essential for smoothly running applications. A probe is generally a REST GET call, but there are other types of probes available. Liveness probes are used to determine when to restart a container. For example, an application that is unhealthy and no longer responding to an API call would be restarted by OpenShift. Readiness probes determine when a container is ready to start receiving traffic. If a readiness probe fails, then the load balancer would deregister that service.

Create Readiness and Liveness Probes

The /info endpoint on the Example Health application is a great way to check whether the application is running and responding to API calls -- it responds with a simple JSON payload.

Navigate to your deployment and choose Actions > Edit Health Checks.

Health Checks

Add a readiness probe:

Readiness

Add a liveness probe:

Liveness

Click Save.

If all works, everything should be the same. Let's check that the probes are really working though.

Inject Failure

Let's edit the probe with a typo to see what happens when it fails. Edit the health check and change the path for the readiness probe to /badpath. Wait a few minutes and check your deployment - you'll notice that 0/1 containers are ready:

Badpath

Dive into your events and you'll see that the probe is failing, causing the platform to try and repeatedly restart your pod.

Deeper Dive

Using health checks gives your OpenShift service layer better reliability and helps you start with a strong foundation.