1. What is CrashLoopBackOff?

CrashLoopBackOff is a pod status in Kubernetes that indicates a container in the pod has crashed repeatedly and Kubernetes is backing off (delaying) before trying to restart it again.

You might see this with:

> kubectl get pods

myapp-pod-xyz   0/1     CrashLoopBackOff   5 (1m ago)   10m

2. Why Does a Pod Enter CrashLoopBackOff?

It occurs when:

• The container crashes (exits with non-zero status) shortly after starting.
• Kubernetes restarts it.
• It crashes again.
• This cycle repeats.

Common Causes:

• Application errors (e.g., missing config/env vars, bad code)
• Failed dependency (e.g., DB not available)
• Wrong command or entrypoint in Dockerfile or YAML
• Files or ports missing
• Health checks failing

3. What Happens Internally in Kubernetes?

When a pod crashes:

1. Kubelet on the node detects the crash.
2. It restarts the container as per the restartPolicy (default is Always).
3. If the crash keeps happening quickly, Kubernetes:
   • Flags it as a CrashLoopBackOff
   • Increases the backoff time between restarts exponentially.

This is done to prevent thrashing and reduce resource wastage.

4. Backoff Policy (Exponential Delay)

Kubernetes uses an exponential backoff strategy to retry restarting the pod:

Restart Attempt	Delay (approximate)
1st	10 seconds
2nd	20 seconds
3rd	40 seconds
4th	80 seconds
…	Max ~5 minutes

So, the more it crashes, the slower Kubernetes tries to restart it.

5. How to Diagnose CrashLoopBackOff?

Step 1: Describe the Pod

kubectl describe pod <pod-name>

Look under Events: for reasons like:

Back-off restarting failed container

Step 2: Check Logs

kubectl logs <pod-name>

If multiple containers:

kubectl logs <pod-name> -c <container-name>

This helps find the root cause like an error stack trace.

Step 3: Use kubectl get and -o wide

kubectl get pod <pod-name> -o wide

May help identify the node or IP it’s running on.