Service exposition with ListenerClasses

The operator deploys a Listener for the Webserver pod. The listener defaults to only being accessible from within the Kubernetes cluster, but this can be changed by setting .spec.webservers.config.listenerClass:

spec:
  webservers:
    config:
      listenerClass: external-unstable  (1)
  schedulers:
    ...
  celeryExecutors:
    ...

1	Specify a ListenerClass, such as `external-stable`, `external-unstable`, or `cluster-internal` (the default setting is `cluster-internal`). This can be set only for the webservers role.