We add support for federated services to the destination controller by adding a new FederatedServiceWatcher. When the destination controller receives a `Get` request for a Service with the `multicluster.linkerd.io/remote-discovery` and/or the `multicluster.linkerd.io/local-discovery` annotations, it subscribes to the FederatedServiceWatcher instead of subscribing to the EndpointsWatcher directly. The FederatedServiceWatcher watches the federated service for any changes to these annotations, and maintains the appropriate watches on the local EndpointWatcher and/or remote EndpointWatchers fetched through the ClusterStore.
This means that we will often have multiple EndpointTranslators writing to the same `Get` response stream. In order for a `NoEndpoints` message sent to one EndpointTranslator to not clobber the whole stream, we make a change where `NoEndpoints` messages are no longer sent to the response stream, but are replaced by a `Remove` message containing all of the addresses from that EndpointTranslator. This allows multiple EndpointTranslators to coexist on the same stream.
Signed-off-by: Alex Leong <alex@buoyant.io>
Alex Leong