Service exposition with ListenerClasses

Apache Druid offers a web UI and an API, both are exposed by the router role. The broker and coordinator roles expose additional API endpoints.

The operator deploys a Listener for the router, broker and coordinator roles. The Listener defaults to only being accessible from within the Kubernetes cluster, but this can be changed by configuring a ListenerClass for specific roles:

spec:
  brokers:
    roleConfig:
      listenerClass: cluster-internal  (1)
  coordinators:
    roleConfig:
      listenerClass: cluster-internal  (1)
  routers:
    roleConfig:
      listenerClass: external-unstable  (1)

1	Specify one of `external-stable`, `external-unstable`, `cluster-internal` or a custom ListenerClass (the default setting is `cluster-internal`).