Get a list of all running pods for own service

Question

The situation

• I have a Spring Boot service running inside Kubernetes
• Multiple instance are running (the kubernetes deployment has multiple replicas configured)
• I have an incoming HTTP from outside the cluster that hits on of the instances
• I want to relay the fact to all other instances

Question

Is there an easy, no external things needed, solution to find a list of "all pods of my service"? I think I remember that this could be possible via DNS resolution but my Google-Fu seems to weak to find something.

Of course I can always to this via some other solution (eg Redis, Kafka, whatever) but since I only need this for a one-off feature I would like to not introduce any moving parts and keep it as simple as possible.

Answer 1

Internal K8s DNS would only get you the IP-address of the service. Luckily, there is the Endpoints resource exactly for the purpose of getting the Pods that back a Service.

With kubectl you can check endpoints out like this:

kubectl get endpoints nginx -o yaml

With this command you get hold of the Pod names:

kubectl get endpoints nginx -o=jsonpath='{.subsets[*].addresses[*].targetRef.name}'

To execute the same thing from your Spring Boot app, you can try to make use of the official Kubernetes Java client library.

Answer 2

You can list all pods behind a service by running

$ kubectl get endpoints <service-name> -o=jsonpath='{.subsets[*].addresses[*].ip}' | tr ' ' '\n' | xargs -I % kubectl get pods --field-selector=status.podIP=%