testbed/pallets__flask/docs/deploying/cgi.rst

CGI
===

If all other deployment methods do not work, CGI will work for sure.
CGI is supported by all major servers but usually has a sub-optimal
performance.

This is also the way you can use a Flask application on Google's `App
Engine`_, where execution happens in a CGI-like environment.

.. admonition:: Watch Out

   Please make sure in advance that any ``app.run()`` calls you might
   have in your application file are inside an ``if __name__ ==
   '__main__':`` block or moved to a separate file.  Just make sure it's
   not called because this will always start a local WSGI server which
   we do not want if we deploy that application to CGI / app engine.

   With CGI, you will also have to make sure that your code does not contain
   any ``print`` statements, or that ``sys.stdout`` is overridden by something
   that doesn't write into the HTTP response.

Creating a `.cgi` file
----------------------

First you need to create the CGI application file.  Let's call it
:file:`yourapplication.cgi`::

    #!/usr/bin/python
    from wsgiref.handlers import CGIHandler
    from yourapplication import app

    CGIHandler().run(app)

Server Setup
------------

Usually there are two ways to configure the server.  Either just copy the
``.cgi`` into a :file:`cgi-bin` (and use `mod_rewrite` or something similar to
rewrite the URL) or let the server point to the file directly.

In Apache for example you can put something like this into the config:

.. sourcecode:: apache

    ScriptAlias /app /path/to/the/application.cgi

On shared webhosting, though, you might not have access to your Apache config.
In this case, a file called ``.htaccess``, sitting in the public directory
you want your app to be available, works too but the ``ScriptAlias`` directive
won't work in that case:

.. sourcecode:: apache

    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f # Don't interfere with static files
    RewriteRule ^(.*)$ /path/to/the/application.cgi/$1 [L]

For more information consult the documentation of your webserver.

.. _App Engine: https://cloud.google.com/appengine/docs/