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.. _mod_wsgi-deployment:
mod_wsgi (Apache)
=================
If you are using the `Apache`_ webserver, consider using `mod_wsgi`_.
.. 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 mod_wsgi.
.. _Apache: http://httpd.apache.org/
Installing `mod_wsgi`
---------------------
If you don't have `mod_wsgi` installed yet you have to either install it
using a package manager or compile it yourself. The mod_wsgi
`installation instructions`_ cover source installations on UNIX systems.
If you are using Ubuntu/Debian you can apt-get it and activate it as
follows:
.. sourcecode:: text
# apt-get install libapache2-mod-wsgi
On FreeBSD install `mod_wsgi` by compiling the `www/mod_wsgi` port or by
using pkg_add:
.. sourcecode:: text
# pkg_add -r mod_wsgi
If you are using pkgsrc you can install `mod_wsgi` by compiling the
`www/ap2-wsgi` package.
If you encounter segfaulting child processes after the first apache
reload you can safely ignore them. Just restart the server.
Creating a `.wsgi` file
-----------------------
To run your application you need a `yourapplication.wsgi` file. This file
contains the code `mod_wsgi` is executing on startup to get the application
object. The object called `application` in that file is then used as
application.
For most applications the following file should be sufficient::
from yourapplication import app as application
If you don't have a factory function for application creation but a singleton
instance you can directly import that one as `application`.
Store that file somewhere that you will find it again (e.g.:
`/var/www/yourapplication`) and make sure that `yourapplication` and all
the libraries that are in use are on the python load path. If you don't
want to install it system wide consider using a `virtual python`_
instance.
Configuring Apache
------------------
The last thing you have to do is to create an Apache configuration file
for your application. In this example we are telling `mod_wsgi` to
execute the application under a different user for security reasons:
.. sourcecode:: apache
<VirtualHost *>
ServerName example.com
WSGIDaemonProcess yourapplication user=user1 group=group1 threads=5
WSGIScriptAlias / /var/www/yourapplication/yourapplication.wsgi
<Directory /var/www/yourapplication>
WSGIProcessGroup yourapplication
WSGIApplicationGroup %{GLOBAL}
Order deny,allow
Allow from all
</Directory>
</VirtualHost>
For more information consult the `mod_wsgi wiki`_.
.. _mod_wsgi: http://code.google.com/p/modwsgi/
.. _installation instructions: http://code.google.com/p/modwsgi/wiki/QuickInstallationGuide
.. _virtual python: http://pypi.python.org/pypi/virtualenv
.. _mod_wsgi wiki: http://code.google.com/p/modwsgi/wiki/
Troubleshooting
---------------
If your application does not run, follow this guide to troubleshoot:
**Problem:** application does not run, errorlog shows SystemExit ignored
You have a ``app.run()`` call in your application file that is not
guarded by an ``if __name__ == '__main__':`` condition. Either
remove that :meth:`~flask.Flask.run` call from the file and move it
into a separate `run.py` file or put it into such an if block.
**Problem:** application gives permission errors
Probably caused by your application running as the wrong user. Make
sure the folders the application needs access to have the proper
privileges set and the application runs as the correct user
(``user`` and ``group`` parameter to the `WSGIDaemonProcess`
directive)
**Problem:** application dies with an error on print
Keep in mind that mod_wsgi disallows doing anything with
:data:`sys.stdout` and :data:`sys.stderr`. You can disable this
protection from the config by setting the `WSGIRestrictStdout` to
``off``:
.. sourcecode:: apache
WSGIRestrictStdout Off
Alternatively you can also replace the standard out in the .wsgi file
with a different stream::
import sys
sys.stdout = sys.stderr
**Problem:** accessing resources gives IO errors
Your application probably is a single .py file you symlinked into
the site-packages folder. Please be aware that this does not work,
instead you either have to put the folder into the pythonpath the
file is stored in, or convert your application into a package.
The reason for this is that for non-installed packages, the module
filename is used to locate the resources and for symlinks the wrong
filename is picked up.
Support for Automatic Reloading
-------------------------------
To help deployment tools you can activate support for automatic
reloading. Whenever something changes the `.wsgi` file, `mod_wsgi` will
reload all the daemon processes for us.
For that, just add the following directive to your `Directory` section:
.. sourcecode:: apache
WSGIScriptReloading On
Working with Virtual Environments
---------------------------------
Virtual environments have the advantage that they never install the
required dependencies system wide so you have a better control over what
is used where. If you want to use a virtual environment with mod_wsgi
you have to modify your `.wsgi` file slightly.
Add the following lines to the top of your `.wsgi` file::
activate_this = '/path/to/env/bin/activate_this.py'
execfile(activate_this, dict(__file__=activate_this))
This sets up the load paths according to the settings of the virtual
environment. Keep in mind that the path has to be absolute.
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