title: uwsgi: What defines the number of workers/process that a django app needs?
body: <p>I have a question for sysadmins and developers.
  I see that uWSGI allows me to set the number or workers or processes when running uWSGI and I had read that it depends on the installed machine, so I have the next questions:</p>
  
  <ol>
  <li>What are the rules that define the number of workers for the machine?</li>
  <li>When used with nginx, does the config <code>worker_processes</code> in nginx.conf affects this?</li>
  <li>When used with Celery and Redis, is the <code>concurrency</code> related to this?</li>
  <li>What about the thread safety in this setup? (I have seen cases in my app where 1 request executes 1 task and the result is 2 calls to celery with this task.)</li>
  </ol>