Separating Web Development Environments in Myghty

On many occasions, its quite useful when developing web applications to have the webapp know whether its in a production/development/testing environment. Rails builds this into the framework and its rather easy to add this toggle throughout a Myghty webapp (or some other Python web framework) as well.

We'll make use of an environment variable so that the webapp environment can be easily configured from lighttpd or Apache. This way just deploying the application under a different handler can toggle the web applications mode of operation. The other thing we'll setup while we're at it, is a variable to keep track of the absolute root of our web application. I've found it quite useful in many cases to be able to get at this information without hardcoding it in, this way its always accurate no matter where the program is.

There's a few rather commands that'll give you the information we're looking for. It took me awhile to find this, so hopefully it'll help someone else out there.

Getting our Absolute Location

Let's assume our directory hierarchy looks like this:

webapp/
   templates/
   components/
   scripts/
      dispatch.fcgi

Maybe you have the script called by mod_python or lighttpd somewhere else, I'm assuming it'll be inside the root of your web application somewhere. In this case, the handler called by lighttpd is dispatch.fcgi. So dispatch.fcgi needs to figure out what the absolute path of the directory is above it.

Here's the code that figures this out:

import os

    Set the prefix to our base path for the webapp
    myloc = os.path.join(os.getcwd(), file)prefix = os.path.normpath(myloc + ‘../..')

The myloc assignment gets the absolute file-name with path of the current file, in this case dispatch.fcgi. Unlike a normal os.getcwd(), this call doesn't care what directory we happen to be in when we import the module, it will always be the absolute file-name of that file.

In case you're curious why this happens, __file__ will return the path of the file relative to the working environment its called from. So combining it with the full path name of the current working environment results in the complete absolute path of the module no matter what the current context or working directory.

The prefix assignment uses the normpath call to strip off the filename, and backup one directory to our webapp root. This leaves us with the absolute path to our webapp/ directory.

Setting and Using the Environment variable

Figuring out if we're in a special runtime environment is quite easy and looks like this:

import os

    MYGHTY_ENV = os.environ.get('MYGHTY_ENV') or 'development'

Now we can just test MYGHTY_ENV to determine whether to contain errors ourself, or drop them to the web (as you would want in development mode). We default to being in development mode, since this is what you'd typically run your webapp in.

To switch it to production mode, here's what the lighttpd config looks like:

fastcgi.server = ( 
   ".fcgi" => (
     "www" => (
        "min-procs" => 2,
        "max-procs" => 4,
        "socket" => "/tmp/webapp.socket",
        "bin-path" => "PATH/TO/webapp/scripts/dispatch.fcgi",
        "bin-environment" => ("MYGHTY_ENV" => "production" ),
        "idle-timeout" => 120
      )
    )
)

To set the extra environment variables with Apache, use mod_env with the SetEnv directive which would look something like this:

# Make sure you have mod_env loaded, this line assumed to be in the VirtualHost
# block of your config
SetEnv MYGHTY_ENV production

At this point, you might've noticed (if you've used Rails) how similar my Fast CGI setup with lighttpd looks when compared to the some of the Rails examples for a lighttpd + Fast CGI setup. This is intentional, as I'm adding a Routes dispatcher to Myghty so it makes sense to layout my web application in a similar directory hierarchy.

Anytime you need to toggle some behavior depending on your webapp's runtime context, just import os and check it as I showed up above.