Open Stack

All,

Presenting a new version of the proof of concept for the 
realtime-communication Horizon blueprint[0]. Here's the code:

https://review.openstack.org/#/q/status:open+project:openstack/horizon+branch:master+topic:bp/realtime-communication,n,z

Following the previous discussion, this iteration listens to the 
OpenStack notifications and passes them using websocket (or one of the 
fallbacks) to the connected browsers. That means adding oslo-incubator 
as a dependency (the RPC bits of it at least).

The code grew a bit more complex, because as far as I can see, the RPC 
helpers in oslo-incubator are deeply intertwined with eventlet, but 
there is no suitable web realtime library built on top of eventlet*.

The available solutions are built on top of gevent or tornado, both of 
which come with their own event loops. In order to both receive 
notifications and push them to the browsers, we need two separate 
threads, one for each event loop.

We're only talking about a 150 lines of code and I don't expect it to 
grow much beyond that, so I'm not really worried about that now. But if 
there are better solutions, please share them.

The original PoC was built on top of gevent and gevent-socketio, neither 
of which is likely to be Python3-compatible any time soon. Since that's 
a requirement for new dependencies, I've switched to Tornado[1] and 
SockJS-tornado[2] that are both compatible with Python 3.

I didn't add the dependencies to openstack/requirements[3] yet but if 
you are fine with this stack, I shall do so and we can start thinking 
about merging this.

To try it out, please run the server:

     ./horizon-realtime.py --config-file etc/horizon/horizon-realtime.conf

navigate to `http://localhost:8080/project/instances` (you can verify 
the WebSocket connection in the JavaScript console) and then launch an 
instance out of band (e.g. via the nova command line). The webpage 
should update automatically when you add, suspend, resume or delete the 
instance.

T.

[0]: https://blueprints.launchpad.net/horizon/+spec/realtime-communication
[1]: http://www.tornadoweb.org/en/stable/
[2]: https://github.com/mrjoes/sockjs-tornado
[3]: https://github.com/openstack/requirements

* eventlet ships with a WebSocket implementation, but it lacks the 
fallback transports, etc. that socket.io and SockJS provide.