Dedicated queues for long-running requests with single unicorn master: question and a possible solution

["Alexander Dymo" <adymo@pluron.com>]

Hey,
I have two major types of requests for my app:
- long-running (10 sec and more, I can differentiate them by url)
- normal (less than 1 sec)

Question is: I'd like to setup the server in a way that:
1) normal requests are served by 15 unicorn workers
2) long-running requests are served by additional 5 unicorn workers with  
their own queue

Separate queue for long-running requests is to prevent people who run long  
requests
consume all workers (for example: hit refresh 20 times or just do too many  
valid but long requests).

Here's the possible solution I came up with and it seems to work.
What do you think about it? Does it have problems I didn't think of?
Are there better ways to do the same thing?


My solution so far:
- in nginx:
   - create two upstream servers
   - configure nginx to pass long-running request to a long-running upstream

   upstream unicorn {
     server unix:/tmp/unicorn.sock;
   }
   upstream long_requests_unicorn {
     server unix:/tmp/long_requests_unicorn.sock;
   }
   server {
     location ~ ^/(long_request_url1|long_request_url2) {
       if (!-f $request_filename) {
         proxy_pass http://long_requests_unicorn;
         break;
       }
     }
     if (!-f $request_filename) {
       proxy_pass http://unicorn;
       break;
     }
   }

- in unicorn configuration file:
   - listen to both sockets in master
   - after forking a child, close the socket it doesn't need to listen to

   worker_processes 20
   listen File.join('/tmp/unicorn.sock')
   listen File.join('/tmp/long_requests_unicorn.sock')

   def assign_to_queue(server, worker)
     queue = case worker.nr
       when  0...15 then '/tmp/unicorn.sock'
       when 15...20 then '/tmp/long_requests_unicorn.sock'
       else raise "Can't find queue for the worker ##{worker.nr}"
     end

     server.listeners = Unicorn::HttpServer::LISTENERS.find_all do |io|
       server.send(:sock_name, io) == queue
     end
   end

   after_fork do |server, worker|
     assign_to_queue(server, worker)
   end
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