How does wordpress.com and other similar services create a subdomain instantly, that is instantly available?

Question

i know almost anything about sub-domains and dns records. i have heard about them and i know just the basics.

Actually, on my server, i do create the subdomain under plesk and then contact my hosting to create the right dns. and in 1-2 days the subdomain is reachable from everywhere (plesk can manage dns automatically, i know, but becose i dont know how does dns exactly works, i prefer to let my hoster handle them)

But.. when you do register on wordpress.com, posterous.com, etc, they create a subdomain like http://yourname.service_name.com that is ready in few seconds.. how?

I know this could be an question hardly to response because my ignorance i dont know how to formulate the question better -.-

Oh, if it can help, my environment must be linux (debian actually)

Answer 1

Most people achieve this by using a Wildcard DNS Record, this gives the appearence of creating subdomains instantly.

---

Once you've got a wildcard DNS setup like this:

 *.example.com          A     77.75.105.197

You need to tell Apache you want all sub domains to be caught by a virtual host, you can do this with ServerAlias:

ServerAlias *.example.com

In PHP you can then look at $_SERVER["SERVER_NAME"] to figure out what subdomain has been used to access the virtual host, you can then have subdomain specific code/content.

Answer 2

Here's the way pastebin.com does this:

• wildcard DNS record points all subdomains at the webserver IP
• apache will send all requests for "unknown" domains to the first virtual host - you make the code on that host capable of doing something interesting with the domain name (in PHP, this is presented as $_SERVER['HTTP_HOST']

That way, no DNS or Apache re-configuration is required.