“CrashLoopBackOff” and how to fix it

So in any larger docker installation, be it Kubernetes or OpenShift, you will encounter pods that crash regularly and enter the “CrashLoopBackOff” status.

$ oc get pod --all-namespaces 
NAMESPACE         NAME                       READY     STATUS             RESTARTS   AGE
[..]
my-project-1      helloworld-11-9w3ud        1/1       Running            0          7h
my-project-2      myapp-simon-43-7macd       0/1       CrashLoopBackOff   3774       9h

Note the container that has status “CrashLoopBackOff” and 3774 restarts.

What does this mean?

So this means the pod is starting, then crashing, then starting again and crashing again. So you will see the symptoms above, namely that the pod STATUS is “CrashLoopBackOff” and there is a growing number of RESTARTS for the pod. This can happen, for example when:

  • In most cases, there is an error as soon as the pod starts (in the initialization of the application for example)
  • The application terminates without attaching a TTY, so Kubernetes thinks the application never ran

How can we fix this?

There is no simple solution for this, as this is specific for your container and whatever application you are running inside the container. But basically, you’ll have to find out why the docker container crashes. The easiest and first check should be if there are any errors in the output of the previous startup, e.g.:

$ oc project my-project-2
$ oc logs --previous myapp-simon-43-7macd

Also, check if you specified a valid “ENTRYPOINT” in your Dockerfile. As an alternative, also try launching your container on Docker and not on Kubernetes / OpenShift.

Comments

Oh no, new comments are currently disabled.
If you want to get in touch with me, please do so via e-mail: