For those of you making an application which supports multi-tenancy, here's some web server configurations you might find handy. A multi-tenancy application in this case is an application who has one code base but supports many organizations/tenants. This typical of many SaaS applications.

One common way to divide up users (or "organizations") with an application is to use subdomains. For example, beanstalkapp.com uses subdomains in such a way. Each organization can have many users. So, for organization "FooBar", the Beanstalkapp domain where users would log into would be http://foobar.beanstalkapp.com.

Now, to do this, we likely want to use the same code base for the entire application. From a web server point of view, this means we want to create a virtual host which can match a wildcard subdomain, so we can have the same application code handle the request. Let's see how to do that in Apache and Nginx.

Apache

For this Apache example, we'll create a virtual host for our marketing site (assuming it's not part of your main application code) and one virtual host for our application.

# The order of the VHosts is important

# Marketing Site
<VirtualHost *:80>

ServerName myapp.io;
ServerAlias www.myapp.io;

DocumentRoot /var/www/marketing-site

</VirtualHost>

The above is just a virtual host like any other. It handles myapp.io and www.myapp.io requests via the ServerName and ServerAlias directives respectively. (The above virtual host isn't complete, you may need to add in some extra directives).

# App Site
<VirtualHost *:80>

ServerName app.myapp.io;
ServerAlias *.myapp.io;

DocumentRoot /var/www/app-site

</VirtualHost>

This virtual host handles a base ServerName of app.myapp.io (you may or may not want to use that yourself) and then uses ServerAlias to match a wildcard subdomain. This directs to a separate DocumentRoot than the marketing site.

If you're using Apache in front of a FastCGI process (simlar to an Nginx setup), you can easily just pass off this request to that as well. That would allow you to combine the previous two virtual hosts into one.

Nginx

Nginx can have a similar setup.

# Marketing Site
server {
    listen 80;

    server_name www.myapp.io myapp.io

    root /var/www/marketing-site

}

The above server block can be used for a marketing home page. Again, it's just a regular old virtual server for Nginx. Nothing special here - it's setup for www.myapp.io and myapp.io domains. (You likely want to use more directives in there - the above example is abbreviated to show only what's necessary).

# App Site
server {
    listen 80;

    # Match *.myapp.io
    server_name  ~^(?<user>.+)\.myapp\.io$;

    root /var/www/app-site

    # Optionally pass the subdomain to the app via
    # fastcgi_param, so it's available as an
    # environment variable
    location / {
        fastcgi_param  USER $user;
        fastcgi_pass 127.0.0.1:9000;
        include fastcgi_params; # fastcgi.conf for version 1.6.1+
    }
}

In this server block, we match a wildcard subdomain. As a bonus, we capture it as well as a $user variable, and can pass that off to our application using a fastcgi_pass directive. This will then become available as an environment variable in our application.

These virtual hosts aren't necessarily complete. Check out the edition on Apache virtual hosts and using Nginx to get more details on what should go in there.