What is Kubernetes Service Internal Traffic Policy?

Question

Accepted Answer

**Internal Traffic Policy** — control intra-cluster traffic routing.

```yaml
apiVersion: v1
kind: Service
metadata:
  name: myapp-local
spec:
  type: ClusterIP
  internalTrafficPolicy: Local
  selector:
    app: myapp
  ports:
  - port: 80
    targetPort: 3000
---
apiVersion: v1
kind: Service
metadata:
  name: myapp-cluster
spec:
  type: ClusterIP
  internalTrafficPolicy: Cluster  # default
  selector:
    app: myapp
  ports:
  - port: 80
    targetPort: 3000
```

```bash
# Check traffic policy
kubectl get svc myapp-local -o jsonpath='{.spec.internalTrafficPolicy}'

# Test Local routing
# Pod on node-1 connects to myapp-local -> only Pod on node-1 is used
# Pod on node-1 connects to myapp-cluster -> any Pod is used

# Check endpoints with hints
kubectl get endpoints myapp-local -o yaml | grep -A 10 hints

# Verify routing behavior
kubectl exec -it my-pod -- curl http://myapp-local.production.svc.cluster.local
kubectl exec -it my-pod -- curl http://myapp-cluster.production.svc.cluster.local

# Check node-local endpoints
kubectl get endpoints myapp-local -o jsonpath='{.subsets[*].addresses[*].nodeName}'
```

**Policies:**
- Cluster (default): route to any endpoint.
- Local: only node-local endpoints.

**Benefits of Local:**
- Preserve source IP.
- Reduce network hops.
- Lower latency.
- Cost optimization (cross-zone traffic).

DevOps: What is Kubernetes Service Internal Traffic Policy?