DNS and Service Discovery

service.namespace.svc.cluster.local

Cluster DNS (CoreDNS) gives every Service a name: web from the same namespace, web.shop-prod from another, or fully web.shop-prod.svc.cluster.local. Applications should connect by these names, configured through environment variables or ConfigMaps, never by IP. Headless Services (clusterIP: None) return the individual pod addresses instead of one virtual IP, used by StatefulSets for stable per-pod names such as db-0.db.

Names a pod can use

From a pod in namespace shop-prod.

web                                   Service "web" in the same namespace
web.shop-prod                          explicit namespace
web.shop-prod.svc.cluster.local        fully qualified
payments.billing                       Service "payments" in namespace "billing"
db-0.db.shop-prod.svc.cluster.local    pod 0 of StatefulSet "db" via headless Service "db"

Configure names, not addresses

Put service URLs in configuration (http://web.shop-prod) so moving or scaling pods never breaks clients.

Quick check: What does a headless Service return in DNS?

• The individual pod addresses instead of a single virtual IP
• Nothing
• The node's IP only
• A public IP