How to fix 404 Not Found in Kubernetes

Run kubectl get ingress -n <namespace> and kubectl describe ingress <ingress-name> to review the configuration. Verify:
- serviceName matches actual Service: kubectl get svc <serviceName> -n <namespace>
- servicePort matches Service port: kubectl get svc <serviceName> -o yaml | grep -A5 ports
- ingressClassName is set correctly (usually "nginx" for NGINX controller)

Run kubectl get pods -l app=<selector-label> -n <namespace> where selector-label matches your Service selector. Verify pods are in Running state: kubectl get pods -n <namespace>. Check pod health: kubectl describe pod <pod-name> -n <namespace>. Look at readiness status—if Not Ready, the pod won't receive traffic.

Connect directly to a pod to verify it responds: kubectl exec -it <pod-name> -n <namespace> -- curl http://localhost:8080/<path>. Replace 8080 with your application port and /<path> with the request path. If the pod responds correctly here but fails through Ingress, the issue is path rewriting.

If your Ingress path doesn't match your application's root, add the rewrite annotation:

metadata:
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - http:
      paths:
      - path: /myapp
        pathType: Prefix
        backend:
          service:
            name: myapp-service
            port:
              number: 8080

This strips /myapp before sending to the backend. Apply with kubectl apply -f ingress.yaml.

Run kubectl get endpoints <service-name> -n <namespace> or kubectl describe svc <service-name> -n <namespace>. The Endpoints section should list pod IPs and ports. If Endpoints is empty or shows <none>, the service has no running pods. If pods exist but aren't in Endpoints, check readiness probes are passing.

Run kubectl logs -n ingress-nginx deployment/nginx-ingress-controller | grep -i "404\|not found". Look for warnings about missing backends or path mismatches. You can also check the access log: kubectl logs -n ingress-nginx <controller-pod> | tail -100 to see request details.

Update Ingress path configuration:

paths:
- path: /myapp(/|$)(.*)
  pathType: ImplementationSpecific
  backend:
    service:
      name: myapp-service
      port:
        number: 8080

Use pathType: Prefix for prefix matching, pathType: Exact for exact matching, or pathType: ImplementationSpecific for regex. Test the regex pattern with online tools before applying.