Oslo.messaging: message proxy

blueprint https://blueprints.launchpad.net/oslo.messaging/+spec/message-proxy-server
https://review.openstack.org/77862 _driver: implement unix domain support
https://review.openstack.org/77863 proxy: implement proxy server

proxy message between two messaging servers or transports

One message server is in openstack control network which openstack servers connect to and another message server is in openstack tenant network which agents connect to. Openstack server wants to send RPC message to agents in tenant networks. The control network isn't directly connected to tenant network. So proxy server relays RPC message over unix domain socket to bypass Linux netns.

                                                     |<-------------------------same node-------------------------------->|
   openstack server <-amqp-> proxy server agent <-unix domain-> proxy server agent <-amqp-> openstack agent
                                                     |<-------netns---------------- >|<-----------------netns----------->|

The supported RPC is cast, call and fanout. notification isn't supported because it's not needed at this moment. But it's easy to add it.

Use Cases

To be filled

design/implementation

To be filled

supported RPC semantics

to be filled

what's added to oslo.messaging