Openshift Health Checks

Question

For Openshift Health checks (Liveness and readiness probes), does the liveness check run after the container is ready. So should the Readiness initial delay be less than the Liveness initial delay.

Please advise.

Thanks B.

Answer 1

The delay specified for both readiness and liveness check is from the start of the deployment. The start of the delay for the liveness check is not dependent on the pod first being ready. Once they start, both run for the life of the pod.

You need to evaluate what you set the delays to based on the role of each check and how you implement the checks.

A readiness probe checks if an application is ready to service requests. It is used initially to determine if the pod has started up correctly and becomes ready, but also subsequently, to determine if the pod IP should be removed from the set of endpoints for any period, with it possibly being added back later if the check is set to pass again, with the application again being ready to handle requests.

A liveness probe checks if an application is still working. It is used to check if your application running in a pod is still running and that it is also working correctly. If the probe keeps failing, the pod will be shutdown, with a new pod started up to replace it.

So having the delay for the liveness check be larger than that for the readiness check is quite reasonable, especially if during the initial startup phase the liveness check would fail. You don't want the pod to be killed off when startup time can be quite long.

You may also want to look at the period and success/failure thresholds.

Overall it is hard to give a set rule as it depends on your application.