I'd like to know how to communicate between processes on a Heroku worker dyno.
We want a Resque worker to read off a queue and send the data to another process running on the same dyno. The "other process" is an off-the-shelf piece of software that usually uses TCP sockets (port xyz) to listen for commands. It is set up to run as a background process before the Resque worker starts.
However, when we try to connect locally to that TCP socket, we get nowhere.
Our Rake task for setting up the queue does this:
task "resque:setup" do
# First launch our listener process in the background
`./some_process_that_listens_on_port_12345 &`
# Now get our queue worker ready, set up Redis backing store
port = 12345
ENV['QUEUE'] = '*'
ENV['PORT'] = port.to_s
Resque.redis = ENV['REDISTOGO_URL']
# Start working from the queue
WorkerClass.enqueue
end
And that works -- our listener process runs, and Resque tries to process queued tasks. However, the Resque jobs fail because they can't connect to localhost:12345 (specifically, Errno::ECONNREFUSED).
Possibly, Heroku is blocking TCP socket communication on the same dyno. Is there a way around this?
I tried to take the "code" out of the situation and just executed on the command line (after the server process claims that it is properly bound to 12345):
nc localhost 12345 -w 1 </dev/null
But this does not connect either.
We are currently investigating changing the client/server code to use UNIXSocket on both sides as opposed to TCPSocket, but as it's an off-the-shelf piece of software, we'd rather avoid our own fork if possible.
