How to debug CrashLoopBackOff when starting a pod in Kubernetes

Recently I tried to deploy a nodeJS application to Amazon EKS and found that the deployment was not ready and the pod was stuck at ``CrashLoopBackOff``. I had no idea what's happening. ```bash $ kubectl get pod NAME READY STATUS RESTARTS AGE app1-789d756b58-k8qvm 1/1 Running 0 13h app2-84cf49f896-4945d 0/1 CrashLoopBackOff 7 13m ``` In order to troubleshoot, I increased kubectl output verbosity to --v=9. For more: [Kubectl output verbosity and debugging](https://kubernetes.io/docs/reference/kubectl/cheatsheet/#kubectl-output-verbosity-and-debugging). ```bash $ kubectl describe pod app2-84cf49f896-4945d -v=9 ``` It should return much info on your console. Search the keyword ``reason`` for more insight. ```json {"reason":"ContainersNotReady","message":"containers with unready status: [app]"} ``` Then I checked Dockerfile and found that the entry point was not correct. It should be app.js in my case. ``` CMD [ "node", "index.js" ] ``` Since I've setup Github Actions to automatically build and push the docker image to Amazon ECR, I could just retrieve the new docker image URI in the console. If you're interested in it, please check out my previous post. Edit the existing deployment by running ``` $ kubectl edit deployment app2 ``` and replace the existing image URI with the new one under spec -> containers -> image. Once it's saved, it will automatically update it. Verify the result. ```bash $ kubectl get pod NAME READY STATUS RESTARTS AGE app1-789d756b58-k8qvm 1/1 Running 0 13h app2-84cf49f896-4945d 1/1 Running 0 14m ``` It's back to Running now.