Alternative frontends for development

When developing on Trac, the installation will typically be served under either tracd or httpd (Apache). When using the latter, there are modules available to enhance the capabilities of Apache: ​mod_python and ​mod-wsgi.

Alternative frontend: mod_python

Virtualenv can be used with Apache and mod_python, but as mod_python will be a system install, it will not be aware of the virtualenv without some configuration. For development this is useful as one Apache server can serve various development versions in a more permanent way. This method will use the system Python, but will add the libraries from the virtualenv.

1. Make a new frontend script that for instance can be stored in the virtualenv bin directory:

   #myvirtualtrac.py
   
   import os
   import site
   site.addsitedir('/path/to/my/virtualenv/lib/python2.4/site-packages')
   
   from trac.web.modpython_frontend import handler
   

2. Update Apache config to use this script. Add or update options according to the default mod_python setup like for instance found in TracModPython:

   # Extend the path so Apache will find your script on path
   PythonPath "['/path/to/my/virtualenv/bin'] + sys.path"
   
   # Make mod_python use new frontend instead of trac.web.modpython_frontend
   PythonHandler myvirtualtrac
   

Alternative frontend: mod_wsgi

With Apache, mod_wsgi is a very good alternative to mod_python. Setting this up follows the same pattern, but for development especially there is one major advantage: it can quite easily be set up to auto-reload on code changes.

1. Update a default TracModWsgi setup to make a daemonised process, and as of mod_wsgi 2.0 (this setup depends on ≥ 2.0) there is built-in support for custom paths and similar. Example of a full VirtualHost configuration:

   <VirtualHost *:80>
       ServerName virtualtrac.local
   
       # Update user and group to be whatever on your system is intended to run the deamon
       # Update the paths to point to virtualenv site-packages (for trac+++) and bin (for script)
       WSGIDaemonProcess virtualtrac user=www group=www threads=25 python-path=/path/to/my/virtualenv/lib/python2.4/site-packages:/path/to/my/virtualenv/bin
   
       WSGIScriptAlias / /path/to/my/virtualenv/bin/virtualtrac.wsgi
   
       <Location />
         WSGIReloadMechanism Process
         WSGIProcessGroup virtualtrac
         # GLOBAL should generally be used instead of SERVER, see http://code.google.com/p/modwsgi/wiki/IntegrationWithTrac
         WSGIApplicationGroup %{GLOBAL}
         Order deny,allow
         Allow from all
       </Location>
   
       # Authentication
       <LocationMatch (/[^/.]+/login)>
         # Note: Change settings with regards to auth method, paths and domain
         AuthType Digest
         AuthName "virtualtrac"
         AuthDigestDomain /trac http://virtualtrac.local
         AuthDigestProvider file
         AuthUserFile /path/to/access.htdigest
         Require valid-user
       </LocationMatch>
   
   </VirtualHost>
   

2. Go to ​ReloadingSourceCode and save the Python script as /path/to/my/virtualenv/bin/monitor.py
3. A basic WSGI frontend script, save as /path/to/my/virtualenv/bin/virtualtrac.wsgi:

   import sys
   sys.stdout = sys.stderr
   
   import os
   os.environ['TRAC_ENV_DIR'] = '/path/to/trac/project'
   # or, alternatively for multiple projects
   #os.environ['TRAC_ENV_PARENT_DIR'] = "/parent/path/to/many/projects"
   os.environ['PYTHON_EGG_CACHE'] = '/path/to/a/temp/to/cache/eggs'
   
   import trac.web.main
   
   import monitor
   monitor.start(interval=1.0)
   # Additionally monitor easy-install.pth to restart whenever installs are done
   monitor.track('/path/to/my/virtualenv/lib/python2.4/site-packages/easy-install.pth')
   
   application = trac.web.main.dispatch_request