Brain should have a look-up service

[bklang]

In a large multi-user environment, it's going to be important that a single Brain entity handles all requests for a given user during a session. It may be that the user provides inputs via IM and receives outputs via Audio, or vice versa. As such, we want to keep that state within a single brain. To achieve this at scale, we will need to be able to dynamically start a Brain for a user on any available host when the first request comes in. If the user has an existing session, we should route all messages to the running Brain appropriate for that user.

The implementation of the lookup service can be made very thin. Some ideas:

• Use DNS to publish the location of the currently running Brain
• Use a consistent hashing algorithm to determine the correct running node for a Brain (see: Memcached)