Table Of Contents

Previous topic

Standard Deployment Pattern

Next topic

Apache Mod-WSGI

Apache Web Server

Warning

You are deploying a web application. This is an inherently risky process. Apache, as with any other web-server, can be configured incorrectly to compromise the security of your machine. You need to either become very familiar with Apache or rely on someone who is to keep your installation safe. At a minimum you need to be sure that you update your server with security patches in a timely manner!

Apache is the most widely-deployed web-server on the planet, and it is well documented. This document simply introduces you to the various features of the server and gives you an idea of how it is normally used with TurboGears 2.1.

Note

Apache is part of the Standard Deployment Pattern for TurboGears 2.1. TurboGears uses the WSGI interface, which can be supported by Apache in a number of ways. The mod_wsgi extension is the recommended implementation for new TurboGears users.

Installation

All major Linux platforms package Apache such that it can be installed with a simple package-manager command. For Debian/Ubuntu machines this command looks like this:

sudo aptitude install apache2

Todo

document Fedora/RHEL installation

which will install Apache and configure it to start automatically on system startup. Apache is configurable via a series of config files installed in (normally) /etc/apache2 with the directories sites-available and sites-enabled being the two most commonly altered.

Deployment Patterns

Normally in an Apache deployment Apache is configured to serve your application’s static files folder directly. This provides a significant performance advantage over having TurboGears serve these files. Apache accesses the files directly from the disk and serves them without needing to load them into memory all at once.

Similarly, Apache will tend to be used to provide the SSL encryption layer for SSL-using sites. Apache’s SSL implementation is reasonably fast and robust, and setup of SSL is well documented for the server.

WSGI Environment

There are 2 major strategies for providing TurboGears with a WSGI environment using Apache. The first is to embed TurboGears into the Apache process with a “captive” WSGI-supporting module. For this strategy:

  • Apache will manage the lifetime of your TurboGears application
  • Normally to restart your application you will have to restart the Apache server
  • Your code needs to be executable by the Apache user, normally www-data
  • Your data directories need to be readable/writable by the Apache user
  • The environment is somewhat restrictive (for instance, you cannot print to stdout)

There are two implementations of this strategy:

  • mod_wsgi – The mod_wsgi apache extension is a very efficient WSGI server, which provides automatic process monitoring, load balancing for multi-process deployments, as well as strong apache integration. Strongly recommended for new users, and is the Standard Deployment Pattern for TurboGears 2.1.
  • FastCGI – when apache extensions are not an option due to web host restrictions (for example, admins want to run suexec on all userspace scripts), you can create a FastCGI dispatcher that invokes the WSGI interface. Generally you should not use this mechanism unless no other mechanism is available.

The second strategy for deploying WSGI with Apache is to have Apache “reverse proxy” or “redirect/rewrite” requests that come in on the main port (80) to a separate TurboGears server process which is running on a “high port” (for example, port 8080) solely on the localhost (private) interface. For this strategy:

  • you are responsible for keeping your TurboGears process running, starting it at boot, and generally making sure that it can receive the requests from the Apache server. See Deploying as a Service/Daemon.
  • You can run the TurboGears process as any user you like, and you can even run it in a “screen” session during development
  • You can easily restart the TurboGears process

There are two implementations of this strategy in Apache:

  • mod_proxy – The mod_proxy extension provides a simple to set-up apache environment that proxies HTTP requests to your TurboGears 2.1 app. It can be used to load balance across multiple machines.
  • mod_rewrite – Very similar to mod_proxy (in fact from the TurboGears side they are identical), but mod_rewrite can be somewhat more complex to setup.

Enable Your Apache Site

Once you have:

You can copy the Apache config file to your Apache sites-available directory, enable it, and restart Apache.

$ sudo cp myapp/apache/myapp /etc/apache2/sites-available
$ sudo chown root:root /etc/apache2/sites-available/myapp
$ sudo a2ensite sitename
$ sudo apache2ctl configtest
$ sudo apache2ctl restart

You should now be able to load your site at the configured location (by default http://localhost/myapp). If your site doesn’t appear, check the Apache error log:

$ less /var/log/apache2/error.log

normally either your Python application will have encountered an error in the .wsgi script. Pay particular attention to the PYTHONPATHS, as this is one of the most common issues that prevents your site from running.

What’s Next