Nginx Ingress returning 502 Bad Gateway — wrong targetPort in Service | Today I Fixed

Nginx ingress was returning 502 Bad Gateway for every request. The pod was Running, the Ingress resource looked fine, and kubectl describe ingress showed no obvious errors.

Root cause: The Service was pointing port: 8080 → targetPort: 8080, but the Node.js app inside the container was actually listening on port 3000. Nginx couldn't reach the backend, so it returned 502.

Fix:

First, verify what port the app is really on:

bash

kubectl exec -it <pod-name> -- curl localhost:3000

Then fix the Service spec:

yaml

# service.yaml — corrected targetPort
spec:
  ports:
    - port: 80
      targetPort: 3000   # was 8080 — must match EXPOSE in Dockerfile
  selector:
    app: my-app

Apply and test:

bash

kubectl apply -f service.yaml
kubectl exec -it <pod-name> -- curl http://my-service.default.svc.cluster.local

Lesson: 502 from Nginx almost always means the Service can't reach the pod — check targetPort matches the actual port the app listens on, not just what's in the Dockerfile EXPOSE.