# DNS and Service Discovery — Kubernetes

Source: https://www.skillbyai.com/en/kubernetes/n-dns

> Find services by name.

## 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.

```text
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.

**Quiz:** What does a headless Service return in DNS?

- [x] The individual pod addresses instead of a single virtual IP
- [ ] Nothing
- [ ] The node's IP only
- [ ] A public IP

*Answer:* The individual pod addresses instead of a single virtual IP. Used for stable per-pod identities.