What is a Service?

Learn that a Service provides network access to Pods.

What is a Service?

Pods come and go and each gets a new IP. A Service offers a stable virtual IP and DNS name in front of a group of pods selected by label; it spreads incoming traffic over the ready pods:

web (Service, 10.96.45.12:80)
 ├─► 10.244.1.5:8080  (web-…-abcde)
 ├─► 10.244.2.7:8080  (web-…-fghij)
 └─► 10.244.1.9:8080  (web-…-klmno)

Another pod in the same namespace reaches this service at http://web.

expose and Endpoints

The fastest way to create a Service for a deployment is kubectl expose. The real pod addresses behind the Service are kept in EndpointSlice objects; if it comes out empty, the selector matches no pods:

$ kubectl expose deployment web --port=80 --target-port=8080
service/web exposed
$ kubectl get endpointslices -l kubernetes.io/service-name=web
NAME        ADDRESSTYPE   PORTS   ENDPOINTS
web-x7k2p   IPv4          8080    10.244.1.5,10.244.2.7,10.244.1.9

Exercise Expose and verify the service

Write three commands: expose the web deployment with --port=80 --target-port=8080; list the services; list the EndpointSlices of the web service with -l kubernetes.io/service-name=web.

Show example solution

kubectl expose deployment web --port=80 --target-port=8080
kubectl get svc
kubectl get endpointslices -l kubernetes.io/service-name=web

Test yourself

Which pods does a Service send traffic to?
- The Deployment's first pod
- Pods matching the selector and Ready
- All pods on the same node
- Pods with the same name
Show answer

Pods matching the selector and Ready — A pod failing its readinessProbe is removed from the endpoint list.

Create a Service for the deployment.

kubectl ____ deployment web --port=80 --target-port=8080

Show answer

kubectl expose deployment web --port=80 --target-port=8080

Match.

Service

Stable address
selector

Target pods
EndpointSlice

Real pod addresses
http://web

DNS name

Next lesson: ClusterIP

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