We recently changed our web server from Thin to Unicorn. This caused our pusher integration to break. After some digging, we found out the cause was something like this:

def send_cool_event
  Pusher["fancy-pants-channel"].trigger_async('cool-event', pants_json)
end

The Pusher trigger_async uses EventMachine for it's asynchronicity (not sure if that's really a word). Unicorn does not have EventMachine so these triggers were no longer actually triggering. Triggering is obviously an important part of the function that a trigger does, so this caused problems.

The way to fix this is to not use Pusher's trigger_async method. Instead handle your own asynchronicity (the more I use that word, the more I think it either really is one, or at least should be). To do this (using delayed job as that's our background worker), we did something like this:

def send_cool_event
  Pusher["fancy-pants-channel"].trigger('cool-event', pants_json)
end
handle_asynchronously :send_cool_event

We are now using trigger instead of trigger_async and we use delayed_job to run that method. Of course you may need to alter your code a bit more to make sure it works well in a delayed_job or whatever else you use.