What is Kubernetes ExternalName Service?

Question

Accepted Answer

**ExternalName** — CNAME alias to external DNS name.

```yaml
apiVersion: v1
kind: Service
metadata:
  name: external-db
  namespace: production
spec:
  type: ExternalName
  externalName: mydb.rds.amazonaws.com
---
apiVersion: v1
kind: Service
metadata:
  name: external-api
  namespace: production
spec:
  type: ExternalName
  externalName: api.external-service.com
---
# Application uses: postgresql://external-db:5432/mydb
# Resolves to CNAME: mydb.rds.amazonaws.com
```

```bash
# Commands
kubectl get svc external-db
kubectl describe svc external-db

# DNS resolution
kubectl exec -it my-pod -- nslookup external-db.production.svc.cluster.local
kubectl exec -it my-pod -- nslookup external-db.production.svc.cluster.local | grep CNAME

# Test connectivity
kubectl exec -it my-pod -- curl http://external-api.production.svc.cluster.local/health

# Switch external target without app changes
kubectl patch svc external-db -p '{"spec":{"externalName":"newdb.rds.amazonaws.com"}}'
```

**Use cases:**
- External database access.
- Third-party API abstraction.
- Migration without code changes.

**Limitations:**
- No port remapping.
- No protocol specification.
- DNS caching can cause stale records.

DevOps: What is Kubernetes ExternalName Service?