Introduction/Issue:
During one of our deployments, we noticed several pods stuck in a CrashLoopBackOff state. This immediately raised alarms since critical services were unavailable. The CrashLoopBackOff loop happens when a container repeatedly crashes right after starting, and Kubernetes keeps trying to restart it. As SREs, our goal was to identify the root cause quickly and restore service availability.
Why it happens/Causes of the issue:
A pod enters CrashLoopBackOff for several reasons:
Application Errors: Misconfigured environment variables or bugs in the application.
Resource Limits: The container is running out of CPU/memory and getting killed (OOMKilled).
Bad Configurations: Missing secrets, incorrect file paths, or failed dependencies.
Permission/Access Issues: The app requires access to resources it doesn’t have.
In our case, the application was failing because it was missing a required environment variable.
How we solved it (Step-by-step):
Check Pod Status
kubectl get pods
The output showed multiple pods stuck in CrashLoopBackOff.
Inspect Pod Logs
kubectl logs
The logs revealed the application was throwing an error:
“Missing DATABASE_URL environment variable.”
Describe the Pod
kubectl describe pod
Confirmed that the env variable wasn’t set in the pod spec.
Fix the Deployment Manifest
We updated the Deployment YAML to include the missing environment variable from a Kubernetes Secret:
env:
– name: DATABASE_URL
valueFrom:
secretKeyRef:
name: app-secrets
key: database_url
Apply the Fix & Restart Pods
kubectl apply -f deployment.yaml
kubectl rollout restart deployment
Verify
After the fix, the pods moved from CrashLoopBackOff to Running, and the service was restored.
Conclusion:
CrashLoopBackOff can be frustrating but is usually straightforward to debug with logs and pod descriptions. The key is systematically checking application errors, resource limits, and configurations. We resolved our issue by fixing a missing environment variable, but setting up proactive monitoring for pod failures and validating manifests before deployment helps prevent such incidents in the future.
Recent Posts