Kubernetes CrashLoopBackOff: Root Cause and Fix (With Real Examples)
NAME READY STATUS RESTARTS AGE
my-app-pod 0/1 CrashLoopBackOff 8 4m
You've seen this. Your pod is stuck in a death loop and you don't know why.
CrashLoopBackOff is not a Kubernetes bug. It means your container started, crashed, Kubernetes tried to restart it, and it crashed again — repeatedly, with increasing back-off delays.
Here's how to find the real cause and fix it.
Step 1: Get the Crash Logs
# Get logs from the PREVIOUS (crashed) container instance
kubectl logs <pod-name> --previous
# If multiple containers in the pod
kubectl logs <pod-name> -c <container-name> --previous
The --previous flag is critical. Without it, you might get logs from the brand-new (about to crash) instance.
Real output examples:
Error: Cannot find module '/app/server.js'
at Function.Module._resolveFilename
→ Wrong entrypoint in Dockerfile
Error: connect ECONNREFUSED 127.0.0.1:5432
→ Database isn't reachable from inside the pod
Killed
→ OOM kill (memory limit exceeded)
Step 2: Describe the Pod
kubectl describe pod <pod-name>
Look at the Events section at the bottom:
Events:
Warning BackOff 2m kubelet Back-off restarting failed container
Warning OOMKilling 3m kubelet Memory limit reached. Killing container my-app
Key events to look for:
-
OOMKilling— memory limit too low -
FailedMount— volume or secret not found -
Pulling+ErrImagePull— image tag doesn't exist -
Unhealthy— liveness probe failing
Step 3: Check Resource Limits
kubectl get pod <pod-name> -o yaml | grep -A 10 resources
resources:
limits:
memory: "64Mi" # This is often way too low for Node apps
cpu: "250m"
requests:
memory: "32Mi"
cpu: "125m"
If your app needs 200Mi to start but the limit is 64Mi, it gets OOM killed before the first request.
Common Root Causes and Fixes
1. Missing Environment Variable
# Check what env vars the app expects
kubectl exec -it <pod-name> -- env | sort
# Compare against your deployment
kubectl get deployment <name> -o yaml | grep -A 20 env
Fix: Add the missing env var to your deployment YAML.
2. Database Connection Refused
# Test connectivity from inside the pod
kubectl exec -it <pod-name> -- nc -zv db-service 5432
Fix: Ensure the database service name matches what your app uses. In Kubernetes, use service names, not IPs.
3. Memory Limit Too Low
# Check current memory usage before it dies
kubectl top pod <pod-name>
Fix:
resources:
limits:
memory: "512Mi" # Increase this
requests:
memory: "256Mi"
4. Wrong Image or Entrypoint
# Test the image locally
docker run --rm -it your-image:tag sh
# Then try running the entrypoint manually
Quick Fix Command Sequence
# 1. Get crash reason
kubectl logs <pod-name> --previous 2>&1 | tail -30
# 2. Check k8s events
kubectl describe pod <pod-name> | grep -A 20 Events
# 3. Check resource usage
kubectl top pod <pod-name>
# 4. Once fixed, force rollout
kubectl rollout restart deployment/<name>
# 5. Watch the new pods
kubectl get pods -w
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