Digital Snake and Family Gossips about (mostly) Python based technologies

Build a WSGI script for mod_wsgi from zc.buildout

Forewords

While building a Flask application with zc.buildout, I have been searching a way to build the script for Apache's mod_wsgi directly from the buildout command.

Being brain dumb, having other emergencies, and being a lazy programmer, I asked to stackoverflow for some hints.

My fellow Gaël Pasgrimaud suggests using collective.recipe.modwsgi but I did not want to add the PasteDeploy monster to my software stack.

So I took time to hack zc.recipe.egg and find how it creates custom scripts. Et voilà...

I found a way to create my custom wsgi script just using the great z3c.recipe.runscript, I already use for other purposes in various projects. z3c.recipe.runscript is a great piece of software that helps creating your own custom small recipes when you don't find what you need in Pypi or have time to create a real zc.buildout recipe. Here are the snips you need to do the same in your project :

A snip of buildout.cfg

[wsgiscript] # Build the wsgi script for mod_wsgi recipe = z3c.recipe.runscript install-script = ${buildout:directory}/buildouthelpers.py:make_wsgi_script update-script = ${:install-script} # Parameters egg = egg.with.wsgiapp script = ${buildout:parts-directory}/wsgiscript/myapp.wsgi app = egg.with.wsgiapp.appobject

The three parameters expected from this custom part are :

egg

The egg name that contains the wsgi app code.

script

The full path to the wsgi script that will be generated, the same path should sit to the right of the WSGIScriptAlias in your Apache config.

app

The Python name of the application object in the above mentioned egg.

And the snip of above referenced buildouthelpers.py:

WSGISCRIPT_TEMPLATE = """\ # -*- coding: utf-8 -*- import sys import os sys.path[0:0] = [ {0} ] _application = None def application(environ, start_response): global _application # Potential app environment setup if _application is None: from {1} import {2} as _application return _application(environ, start_response) """ def make_wsgi_script(recipe, buildout): """Build the script for Apache/mod_wsgi """ # Late import: zc.recipe.egg may not be installed when executing 1st # function from zc.recipe.egg.egg import Eggs app_egg = recipe['egg'] wsgi_filepath = recipe['script'] app_mod, app_obj = recipe['app'].rsplit('.', 1) # 'a.b.c.d' -> 'a.b.c', 'd' reqs, ws = Eggs(buildout, app_egg, recipe).working_set() egg_paths = [pkg.location for pkg in ws] src_egg_paths = ',\n'.join([" '{0}'".format(path) for path in egg_paths]) with open(wsgi_filepath, 'w') as fh: fh.write(WSGISCRIPT_TEMPLATE.format(src_egg_paths, app_mod, app_obj)) return

Some assumptions without which none of this works:

Your wsgi app sits in the egg.with.wsgiapp egg.
This egg.with.wsgiapp egg is installed in another buildout part using zc.recipe.egg recipe (or another one that relies on it), and this part is executed before [wsgiscript].
All requirements for egg.with.wsgiapp must sit in its setup() parameter install_requires and not in a pip requirements file.

Hope this will help others who fell in a similar situation. Any question or improvement suggestion is welcome.

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