Using (Fast)CGI for non-PHP websites
You're not stuck with PHP if you want to make a dynamic website. You can use all sorts of frameworks and programming languages with ULYSSIS, as long as it has CGI or FastCGI support.
If you want to use a certain programming language or framework, and you can't get it to work, don't hesitate to contact us at ulyssis@ulyssis.org. We will of course not write any code for you, but we can give you some pointers or directions.
CGI
CGI is a simple way to create a dynamic website. We use Apache's mod_cgid to provide support for CGI. Note, however, that CGI is inefficient and in general we recommend you to use a framework together with FastCGI. There are many frameworks, ranging from very simple and lightweight, to more complex and feature rich.
If, for example, you want Apache to interpret all files with the extension .cgi as CGI scripts, use the following .htaccess file (to be placed in your www folder):
Options +ExecCGI AddHandler cgi-script .cgi
Here's an example of a very simple Python CGI script (called hello.cgi):
#!/usr/bin/env python print 'Content-Type: text/plain\n' print 'Hello world!'
CGI scripts need to be executable, otherwise they won't work:
chmod +x hello.cgi
FastCGI
We use Apache's mod_fcgid to provide support for FastCGI.
In order to use FastCGI, you will generally need a starter script specific to your framework and application. Just do a web search for "framework mod_fcgid", where you framework is the framework you're using, and you will find good instructions. There's a Django example below.
You'll want to treat this starter script as a mod_fcgid script, and usually, you'll want to redirect everything to this script, so you can use an .htaccess file that looks like this:
Options +ExecCGI
AddHandler fcgid-script .fcgi
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ starter.fcgi/$1 [QSA,L]
Replace starter.fcgi with the name of your starter script. Don't forget to make your starter script executable:
chmod +x starter.fcgi
The starter script must be located in the same folder as the .htaccess file.
It is adviced to only place the fcgi starter script, .htaccess and static files (images, stylesheets) inside the document root.
Startup time and persistency
It is important to keep in mind that our Apache webworkers will only run your start script when a request is made. As soon as that first request has been received, it will try and keep a few instances of your application around for future use. This of course affects how you restart your application after changes (see below), but also means that applications with a longer start up time (for example a language such as Python combined with a larger framework) will experience an initial slow request. This slow startup is obviously not a factor for faster languages such as Haskell, C++ or Go.
Sadly, Apache is unable to have FastCGI processes persist beyond a reload or restart. This means in practice that every night around 6h25 when the logs are rotated, which requires Apache to be reloaded, all running fcgi processes will be gracefully terminated. The same thing happens when we make changes to the Apache configuration when a new website or user is added.
For those who have a very high startup time and don't generate enough traffic to not experience issues with this behaviour, it's possible to use a cronjob to visit the website every night at 6h30 or 7h, or even hourly.
Restarting your application
If you've changed your application, you will need to restart it for these changes to take effect. However, because you're editing the application on a different server than were it is running, you do not have access to the running process. You'll have to create some sort of mechanism to restart the process.
In the Django example below, the starter script has been written so that when it is changed, the application is automatically restarted within 1 second. The same mechanism can be applied to other Python sites. You can change the modification date without actually changing the contents of the starter script by using touch:
touch starter.fcgi
Replace starter.fcgi with the name of your starter script.
Example: Django
If you want to make a website using Django, we recommend that you use a virtualenv. This tool is already preinstalled on our shell servers.
You can use the following steps to get up and running with Django at ULYSSIS:
- Log in to a shell server
- Create a new virtualenv, you can create one in ~/.venv, for example:
virtualenv ~/.venv
Or, for Python 3:
virtualenv ~/.venv --python=python3
- Activate this virtualenv:
. ~/.venv/bin/activate
-
Install Django inside of this virtualenv:
pip install django
-
Create a new Django project:
django-admin.py startproject mysite
Replace mysite with your project's desired name.
-
Install flup for FastCGI:
pip install flup6
-
Put an .htaccess file in your site's directory, e.g. the www folder:
Options +ExecCGI AddHandler fcgid-script .fcgi RewriteEngine On RewriteCond %{REQUEST_FILENAME} !-f RewriteRule ^(.*)$ mysite.fcgi/$1 [QSA,L] -
Create the starter script (replace user with org if you are an organization, and username with your ULYSSIS username):
<syntaxhighlight lang="php">#!/home/user/username/.venv/bin/python import sys, os, os.path from threading import Thread this_file = os.path.realpath(__file__) site_dir = '/home/user/username/mysite' sys.path.insert(0, site_dir) os.chdir(site_dir) os.environ['DJANGO_SETTINGS_MODULE'] = 'mysite.settings' def stat_thread(): import time, os, signal start_mtime = os.stat(this_file).st_mtime while True: cur_mtime = os.stat(this_file).st_mtime if cur_mtime != start_mtime: os.kill(os.getpid(), signal.SIGTERM) time.sleep(1) Thread(target=stat_thread).start() from django.core.servers.basehttp import get_internal_wsgi_application from flup.server.fcgi import WSGIServer WSGIServer(get_internal_wsgi_application(), debug=False).run() </syntaxhighlight>Call this script mysite.fcgi.
-
Make the starter script executable:
chmod +x mysite.fcgi
- Go to username.ulyssis.be (or whatever URL you chose to use), and it should show you the default "Welcome to Django" page.
This guide was based on, and you can find more information in the official Django documentation:
