View source for 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 [mailto:ulyssis@ulyssis.org 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 [http://httpd.apache.org/docs/2.4/mod/mod_cgid.html 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 <code>.cgi</code> as CGI scripts, use the following <tt>.htaccess</tt> file (to be placed in your <code>www</code> folder):
<pre>Options +ExecCGI
AddHandler cgi-script .cgi</pre>

Here's an example of a very simple Python CGI script (called <code>hello.cgi</code>):
<pre>#!/usr/bin/env python

print 'Content-Type: text/plain\n'
print 'Hello world!'</pre>

CGI scripts need to be executable, otherwise they won't work:
<pre>chmod +x hello.cgi</pre>

==FastCGI==

We use Apache's [http://httpd.apache.org/mod_fcgid/mod/mod_fcgid.html mod_fcgid] to provide support for FastCGI.

In order to use FastCGI, you will generally need a starter script specific to your programming languae, framework or application. Just do a web search for "''keyword'' mod_fcgid", where ''keyword'' is the programming language, framework or application you're planning to use, and you will often find good instructions. We've included some examples below

You'll want to treat this starter script as a <code>mod_fcgid</code> script, and usually, you'll want to redirect everything to this script, so you can use an <code>.htaccess</code> file that looks like this:
<syntaxhighlight lang="apache">Options +ExecCGI
AddHandler fcgid-script .fcgi
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ starter.fcgi/$1 [QSA,L]</syntaxhighlight>
Replace ''starter.fcgi'' with the name of your starter script. Don't forget to make your starter script executable:
<pre>chmod +x starter.fcgi</pre>
The starter script must be located in the same folder as the <code>.htaccess</code> file.

{{warning|Warning!|Do not place sensitive files inside the web accessible folder. Make sure they are located in a folder outside the document root, or they will be downloadable through the webserver.}}
It is adviced to only place the fcgi starter script, <code>.htaccess</code> 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 [[Managing_Cron_jobs | 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 where 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 and Go examples 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 <code>touch</code>:
<pre>touch starter.fcgi</pre>
Replace <code>starter.fcgi</code> with the name of your starter script.

=== Examples ===
==== Python and Django ====

If you want to make a website using Python and [https://www.djangoproject.com/ Django], we recommend that you use a virtual environment. You can use the following steps to get up and running with Django on your ULYSSIS hosting account.

<ol>
<li>[[Accessing shell servers over SSH|Log in to a shell server]]</li>
<li>Create a new virtualenv, you can create one in <code>~/.venv</code>, for example:
<pre>python3 -m venv ~/.venv</pre>
</li>
<li>Activate this virtualenv:
<pre>. ~/.venv/bin/activate</pre>
</li>
<li>
Install Django and flup for FastCGI inside of this virtualenv:
<pre>pip install django flup6</pre>
</li>
<li>
Create a new Django project:
<pre>django-admin startproject mysite</pre>
Replace ''mysite'' with your project's desired name.
</li>
<li>
Edit the allowed hosts in your Django project's settings, in <code>mysite/mysite/settings.py</code>. Look for the line <code>ALLOWED_HOSTS = []</code> and replace it with:
<pre>
ALLOWED_HOSTS = [ 'username.ulyssis.be', 'username.studentenweb.org' ]
</pre>
Use your ULYSSIS username in place of ''username''.
</li>
<li>
Put an <code>.htaccess</code> file in your site's directory, e.g. the <code>www</code> folder:
<pre>Options +ExecCGI
AddHandler fcgid-script .fcgi
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ mysite.fcgi/$1 [QSA,L]</pre>
</li>
<li>
Create the starter script (replace <code>user</code> with org if you are an organization, and <code>username</code> with your ULYSSIS username):
<syntaxhighlight lang="python">#!/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 <code>mysite.fcgi</code>.
</li>
<li>
Make the starter script executable:
<pre>chmod +x mysite.fcgi</pre>
</li>
<li>
Go to ''username''.ulyssis.be (or whatever URL you chose to use), and it should show you the default "Welcome to Django" page.
</li>
</ol>

This guide was based on, and you can find more information in the official Django documentation:
* [https://docs.djangoproject.com/en/stable/intro/tutorial01/ The Django tutorial]
* [https://flask.palletsprojects.com/en/1.1.x/deploying/fastcgi/ Flask documentation for FastCGI]

==== Go ====
To make a website or web application in Go and host it on your ULYSSIS hosting account, you can use the standard library ''fcgi'' package. 

<ol>
<li> [[Accessing shell servers over SSH|Log in to a shell server]]</li>
<li> Put an <code>.htaccess</code> file in your site's directory (e.g. the <code>www</code> folder) with a reference to your executable. Here we've chosen <code>mysite.fcgi</code>, but you can adapt this to your liking.
<pre>Options +ExecCGI
AddHandler fcgid-script .fcgi
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ mysite.fcgi/$1 [QSA,L]</pre>
</li>
<li> Write your code, and compile the binary to <code>mysite.fcgi</code>. Below you can find a basic example of how to register two handlers (of which one is the fallback), then start the FastCGI client, and finally have a function (which is called as a goroutine) to check if the binary has been replaced so old processes don't stick around.
<syntaxhighlight lang="go">package main

import (
	"fmt"
	"net/http"
	"net/http/fcgi"
	"os"
	"path/filepath"
	"time"
)

func uri_interesting(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusOK)
	fmt.Fprintln(w, "<h1>Oh, seems like this link isn't that interesting after all</h1>")
	fmt.Fprintln(w, "<p>Back to the <a href=\"/\">Homepage</a></p>")
}

func uri_default(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		w.WriteHeader(http.StatusNotFound)
		fmt.Fprintln(w, "<h1>This page doesn't exist</h1>")
		fmt.Fprintln(w, "<p>Back to the <a href=\"/\">Homepage</a></p>")
	} else {
		w.WriteHeader(http.StatusOK)
		fmt.Fprintln(w, "<h1>Welcome to this testwebsite!</h1>")
		fmt.Fprintln(w, "<p>This website is written in Go but doesn't really do much.")
		fmt.Fprintln(w, "Feel free to visit this <a href=\"/interesting/link\">Interesting link</a> or this <a href=\"/non-existent/link\">non-existent link</a>.</p>")
	}
}

func main() {
	go check_selfreplacement()
	http.HandleFunc("/interesting/link", uri_interesting)
	http.HandleFunc("/", uri_default)
	if err := fcgi.Serve(nil, nil); err != nil {
		panic(err)
	}
}

func check_selfreplacement() {
	fcgi_location, _ := os.Executable()
	fcgi_location, _ = filepath.EvalSymlinks(fcgi_location)
	start_stat, _ := os.Stat(fcgi_location)
	for {
		current_stat, _ := os.Stat(fcgi_location)
		if start_stat.ModTime() != current_stat.ModTime() {
			os.Exit(0)
		}
		time.Sleep(1 * time.Second)
	}
}
</syntaxhighlight>
If you want to give this example a try, save it as <code>mysite.fcgi.go</code> and then use <code>go build mysite.fcgi.go</code> to compile it.
</li>
<li>Visit your website to verify everything works</li>
</ol>

[[Category:Webserver]]