Headless Services

A headless service is a service that does not have a cluster IP.

Instead of connecting to the service's cluster IP, the client should connect to the service's pod IP directly.

Headless service descriptor

Put clusterIP: None in the service's spec.

apiVersion: v1
kind: Service
metadata:
  name: kubia-headless
spec:
  # make the service headless
  clusterIP: None
  ports:
    - port: 80
      targetPort: 8080
  selector:
    app: kubia

Working with headless services

Getting all of a service's pod IPs

If you perform a DNS query on a headless service, instead of it returning just one A record, it will return multiple A record (one for each of the service's pod IP).

# Creating a pod with `nslookup` and `dig` binaries
kubectl run dnsutils --image=tutum/dnsutils --command -- sleep infinity
# pod/dnsutils created

# Example of hitting a normal service
# One A record (the service's cluster IP)
kubectl exec dnsutils -- nslookup kubia
# ...
# Name:    kubia.default.svc.cluster.local
# Address: 10.111.249.153

# Example of hitting a headless service
# Multiple A records (the service's pod IPs)
kubectl exec dnsutils -- nslookup kubia-headless
# ...
# Name:    kubia-headless.default.svc.cluster.local
# Address: 10.108.1.4
# Name:    kubia-headless.default.svc.cluster.local
# Address: 10.108.2.5

References

• Kubernetes in Action (Marko Lukša) — Chapter 5. Services: enabling clients to discover and talk to pods