<a href="http://flask.pocoo.org/docs/design/">small core and easy-to-extend philosophy</a>. </p>

<p><a href="http://flask.pocoo.org/" style="border: none;"><img src="/img/flask.jpg" width="100%" alt="Official Flask logo. Flask Artwork License." class="technical-diagram"></a></p>

<h1>Green Unicorn (Gunicorn)</h1>

<p><a href="http://gunicorn.org/">Green Unicorn</a>, commonly shortened to "Gunicorn",

is a <a href="/wsgi-servers.html">Web Server Gateway Interface (WSGI) server</a>

implementation that is commonly used to run Python web applications.</p>

<p><a href="http://gunicorn.org/" style="border: none;"><img src="/img/gunicorn-logo.jpg" width="100%" alt="Official Green Unicorn (Gunicorn) logo." class="technical-diagram"></a></p>

<h2>Why is Gunicorn important?</h2>

<p>Gunicorn is one of many WSGI server implementations, but it's particularly

important because it is a stable, commonly-used part of

<a href="/deployments.html">web app deployments</a> that's powered some of the

largest Python-powered web applications in the world, such as

<a href="http://instagram-engineering.tumblr.com/post/13649370142/what-powers-instagram-hundreds-of-instances">Instagram</a>.</p>

<p>Gunicorn implements the

<a href="https://www.python.org/dev/peps/pep-3333/">PEP3333 WSGI server standard specification</a>

so that it can run Python web applications that implement the application

interface. For example, if you write a web application with a

<a href="/web-frameworks.html">web framework</a> such as <a href="/django.html">Django</a>,

<a href="/flask.html">Flask</a> or <a href="/bottle.html">Bottle</a>, then your application

implements the WSGI specification. </p>

<h2>How does Gunicorn know how to run my web app?</h2>

<p>Gunicorn knows how to run a web application based on the hook between the

WSGI server and the WSGI-compliant web app.</p>

<p>Here is an example of a typical Django web application and how it is run

by Gunicorn. We'll use the

<a href="https://github.com/makaimc/compare-python-web-frameworks/tree/master/django_defaults">django_defaults</a>

as an example Django project. Within the <a href="https://github.com/makaimc/compare-python-web-frameworks/tree/master/django_defaults/django_defaults">django_defaults</a>

project subdirectory, there is a short <a href="https://github.com/makaimc/compare-python-web-frameworks/blob/master/django_defaults/django_defaults/wsgi.py">wsgi.py</a>

file with the following contents:</p>

<div class="highlight"><pre><span class="sd">&quot;&quot;&quot;</span>

<span class="sd">WSGI config for django_defaults project.</span>

<span class="sd">It exposes the WSGI callable as a module-level variable named ``application``.</span>

<span class="sd">For more information on this file, see</span>

<span class="sd">https://docs.djangoproject.com/en/1.8/howto/deployment/wsgi/</span>

<span class="sd">&quot;&quot;&quot;</span>

<span class="kn">import</span> <span class="nn">os</span>

<span class="kn">from</span> <span class="nn">django.core.wsgi</span> <span class="kn">import</span> <span class="n">get_wsgi_application</span>

<span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="o">.</span><span class="n">setdefault</span><span class="p">(</span><span class="s">&quot;DJANGO_SETTINGS_MODULE&quot;</span><span class="p">,</span> <span class="s">&quot;django_defaults.settings&quot;</span><span class="p">)</span>

<span class="n">application</span> <span class="o">=</span> <span class="n">get_wsgi_application</span><span class="p">()</span>

<p>That <code>wsgi.py</code> file was generated by the <code>django-admin.py startproject</code> command

when the Django project was first created. Django exposes an <code>application</code>

variable via that <code>wsgi.py</code> file so that a WSGI server can use <code>application</code>

as a hook for running the web app. Here's how the situation looks visually:</p>

<p><img src="/img/gunicorn-django-wsgi.png" alt="Gunicorn WSGI server invoking a Django WSGI application." width="100%" class="technical-diagram" /></p>

<h2>What's a "pre-fork" worker model?</h2>

<p>Gunicorn is based on a pre-fork worker model, compared to a worker model

architecture. The pre-work worker model means that a master thread spins up

workers to handle requests but otherwise does not control how those workers

perform the request handling. Each worker is independent of the controller.</p>

<h3>Gunicorn resources</h3>

<p><a href="http://adambeagle.com/blog/deploying-django-17-ubuntu/">Deploying Django 1.7 on Ubuntu with DigitalOcean with PostgreSQL, Nginx, and Gunicorn</a>

is a detailed walkthrough that uses Green Unicorn as the WSGI server part of

the deployment.</p>

<p>The <a href="http://www.deploypython.com/">Full Stack Python Guide to Deployments</a>

provides detailed step-by-step instructions for deploying Gunicorn as part

of an entire Python web application deployment.</p>

<p><a href="http://prakhar.me/articles/flask-on-nginx-and-gunicorn/">Flask on Nginx and Gunicorn</a>

combines the <a href="/nginx.html">Nginx web server</a> with Gunicorn in a deployment

to serve up a Flask application.</p>

<p>The answers to the question "<a href="http://stackoverflow.com/questions/16857955/running-django-with-gunicorn-best-practice">what's the best practice for running Django with Gunicorn?</a>"

provide some nuance for how Gunicorn should be invokin the callable application

variable provided by Django within a deployment.</p>

<p><a href="http://linoxide.com/linux-how-to/install-django-gunicorn-nginx-freebsd-10-2/">How to Install Django with Gunicorn and Nginx on FreeBSD 10.2</a>

is a tutorial for FreeBSD, which is not often used in walkthroughs compared to

the frequency that Ubuntu and CentOS tutorials appear.</p>