Kubernetes Ingress 503 Service Unavailable: 5 Causes and Fixes

# Check if pods are running
kubectl get pods -n <namespace> -l app=<your-app>
 
# Check the Ingress
kubectl describe ingress <name> -n <namespace>
 
# Check nginx ingress controller logs
kubectl logs -n ingress-nginx -l app.kubernetes.io/name=ingress-nginx --tail=50 | grep 503
 
# Check if the service has endpoints
kubectl get endpoints <service-name> -n <namespace>
# If ENDPOINTS shows "none" — that is your problem

kubectl get endpoints myapp-service -n production
# NAME             ENDPOINTS       AGE
# myapp-service    <none>          5m    ← Problem!

# Service selector
kubectl get svc myapp-service -n production -o jsonpath='{.spec.selector}'
# {"app":"myapp","version":"v1"}
 
# Pod labels
kubectl get pod myapp-xyz -n production -o jsonpath='{.metadata.labels}'
# {"app":"myapp","version":"v2"}  ← Mismatch! version label differs

# Broken Ingress
spec:
  rules:
  - host: myapp.example.com
    http:
      paths:
      - backend:
          service:
            name: myapp-svc        # Wrong — service is named 'myapp-service'
            port:
              number: 8080         # Wrong — service port is 80

kubectl get svc -n production | grep myapp
# myapp-service   ClusterIP   10.0.0.1   <none>   80/TCP
 
kubectl describe ingress myapp-ingress -n production | grep -A 10 "Rules:"
# Shows what the Ingress is targeting

spec:
  rules:
  - host: myapp.example.com
    http:
      paths:
      - backend:
          service:
            name: myapp-service    # Exact service name
            port:
              number: 80           # Service port, not container port

kubectl get pods -n production
# NAME               READY   STATUS    RESTARTS
# myapp-xyz-abc      0/1     Running   0         ← 0/1 = not ready
 
# Check why
kubectl describe pod myapp-xyz-abc -n production | grep -A 15 "Readiness:"
# Shows readiness probe config and failure reason

readinessProbe:
  httpGet:
    path: /health
    port: 8080
  initialDelaySeconds: 30     # Give app time to start
  periodSeconds: 10
  failureThreshold: 3
  timeoutSeconds: 5           # Increase if app is slow to respond

kubectl exec -it myapp-xyz-abc -n production -- curl -s localhost:8080/health
# If this fails or hangs — that is your readiness probe failure

kubectl get ingressclass
# NAME    CONTROLLER             PARAMETERS   AGE
# nginx   k8s.io/ingress-nginx   <none>       10d

# Add annotation or ingressClassName
metadata:
  annotations:
    kubernetes.io/ingress.class: nginx    # Older syntax
 
# OR (newer syntax)
spec:
  ingressClassName: nginx

kubectl get networkpolicy -n production

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-ingress
  namespace: production
spec:
  podSelector:
    matchLabels:
      app: myapp
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
          kubernetes.io/metadata.name: ingress-nginx
    ports:
    - port: 8080

# 1. Check pod health
kubectl get pods -n production -l app=myapp
# Look for READY: 1/1 and STATUS: Running
 
# 2. Check endpoints
kubectl get endpoints myapp-service -n production
# Should show IP addresses, not <none>
 
# 3. Check service selector matches pod labels
kubectl get svc myapp-service -n production -o yaml | grep -A 5 selector
kubectl get pods -n production -l app=myapp --show-labels
 
# 4. Test direct access to pod (bypass Ingress)
kubectl port-forward pod/myapp-xyz -n production 8080:8080
curl localhost:8080/health
# If this works, problem is between Ingress and Service
 
# 5. Test via Service (bypass Ingress)
kubectl run -it --rm debug --image=curlimages/curl --restart=Never -- \
  curl myapp-service.production.svc.cluster.local/health
# If this works, problem is in the Ingress config
 
# 6. Check Ingress controller logs
kubectl logs -n ingress-nginx -l app.kubernetes.io/name=ingress-nginx --tail=100 | grep -i error