🚨 CrashLoopBackOff in Kubernetes: Why Your Pods Keep Restarting (And How I Solved It)

Hey there, fellow dev! 👋

So the other day, I was deploying one of my apps into a Kubernetes cluster — feeling all proud and DevOps-y — and then…
Boom. CrashLoopBackOff slapped me in the face.

If you’ve ever seen this error, you know it’s frustrating. It sounds scary and dramatic — like something exploded. But in reality, it’s Kubernetes just trying (and failing) to keep your app alive.

Let’s walk through what it means, why it happens, and how I fixed it — so you can skip the headache.

❓ What is CrashLoopBackOff?

A CrashLoopBackOff means your pod starts, crashes, and then restarts — over and over again. Kubernetes tries to keep it alive, but since it keeps failing, it eventually slows down the restart cycle, hence the term “BackOff.”

Think of it as Kubernetes saying:

“Something’s broken in here… I’ll keep trying, but I need a break.”

🔍 Real-Life Debugging: My CrashLoopBackOff Journey

I first ran:

kubectl get pods

And saw something like this:

NAME                                   READY     STATUS             RESTARTS      AGE
mern-app-deployment-7547fdcbcf-lk9mn   0/1       CrashLoopBackOff   5 (40s ago)   3m

The status section will show the pod status. If the pod has the CrashLoopBackOff status, it will show as not ready, (as shown below 0/1), and will show more than 0 restarts.

To get more info:

kubectl describe pod mern-app-deployment-7547fdcbcf-lk9mn

Then the logs:

kubectl logs mern-app-deployment-7547fdcbcf-lk9mn

And there it was — a fatal error in my Node.js backend:

“Missing environment variable: DB_URI”

Classic. I had missed setting a critical environment variable for MongoDB.

🔥 Top Reasons for CrashLoopBackOff (And How to Fix Them)

Here’s a combo of what I experienced and some other common causes from the field:

1. 🧾 Misconfiguration of the Container

Typos in YAML, wrong paths, missing configs… it's easy to slip.

Fix:

• Double-check your Deployment YAML.

• Validate syntax with kubectl apply --dry-run=client -f deployment.yaml

• Use kubectl logs for container-level errors.

2. 🚫 Out of Memory or Resources

Your app might be getting killed by the OS if it exceeds memory/CPU limits.

Fix: Add proper limits:

resources:
  limits:
    memory: "256Mi"
    cpu: "500m"
  requests:
    memory: "128Mi"
    cpu: "250m"

Monitor with:

kubectl top pod

3. 🔁 Liveness/Readiness Probe Misconfigurations

Sometimes your app takes longer to start, and K8s kills it thinking it's dead.

Fix:

livenessProbe:
  httpGet:
    path: /health
    port: 3000
  initialDelaySeconds: 15
  periodSeconds: 10
  failureThreshold: 5

Tweak timings to suit your app.

4. 🔐 Incorrect or Missing Environment Variables

Just like in my case — a missing DB_URI crashed the entire container.

Fix: Set them properly in your Deployment:

env:
  - name: DB_URI
    valueFrom:
      secretKeyRef:
        name: db-secrets
        key: uri

5. ⚠️ Two Containers Using Same Port in a Pod

If multiple containers are in one pod, they must not bind to the same port.

Fix: Assign unique ports in your config.

6. 📦 Non-existent Resources or Packages

If your container references a missing script, file, or volume — it’ll crash.

Fix: Ensure all mounted volumes and paths are valid. Check volumeMounts in your Deployment YAML.

7. ❗ Wrong Command or Entrypoint

Your container might be starting with a faulty CMD or ENTRYPOINT.

Fix: Test locally:

docker run your-image

Fix the Dockerfile or override the command in the YAML.

8. ❌ Filesystem is Read-only

If your app needs to write to a path and it’s read-only — kaboom.

Fix:

• Check volume mounts.

• Use emptyDir for temporary write space:

volumes:
  - name: temp-storage
    emptyDir: {}

9. 🌐 DNS or Networking Issues

Your pod might be trying to reach an endpoint that doesn’t exist or DNS is failing.

Fix: Try:

nslookup <service-name>

Make sure kube-dns is running:

kubectl get pods -n kube-system

10. 🧠 Command Line Args or Flags are Wrong

You might’ve missed passing in required flags to your app.

Fix: Add or correct them in the command or args section of the YAML.

🧪 Pro Tip: Test the Image Locally

Before deploying, always try:

docker run your-image

If it crashes locally, fix it before even touching Kubernetes.

✅ Final Debug Checklist

• kubectl describe deployment

• kubectl describe pod

• kubectl logs

• All ENV vars set?

• Configs and volumes mounted correctly?

• Liveness/readiness probes okay?

• Resources (CPU/mem) properly set?

• No port conflicts in pod?

📘 TL;DR

CrashLoopBackOff is just Kubernetes doing its job — trying to keep your app alive and failing gracefully.

Once you learn how to read the signs (logs, probes, configs), it becomes easier to debug and fix.
And now that I’ve solved it (after sweating through it), I hope this post helps you do the same — faster.

💬 Let’s Connect!

If you found this helpful, feel free to:

• Drop a comment

• Share it with someone who need it

• Or send me a message — always happy to learn together 🙌