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 (e.g. 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.
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.
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=%