help regarding setting up pseudo/fake subdomains on apache - apache

Question

First of all, sorry if I got the term 'pseudo subdomain' wrong.
what I am trying to achieve is this-
When someone registers on my application, they get a new url like..
yourname.myapp.tld
I dont want to use the subdomain system for this. To be frank, I dont know how the subdomains exactly work but it guess it requires a folder per subdomain inside the document root and then the server redirects the requests there.
Can this be achieved by doing something like -
when a visiter types any subdomain, (anything.myapp.tld), he is able to access myapp . In the index.php file i will explode the $_SERVER['HTTP_HOST'] to get the subdomain which i will store in session and will thereafter act as an identifier for that user. Ideally i wouldnt want to create any vhosts or add many lines to the hosts file. Can this be achieved with just one vhost?
Is this possible with mod rewrite or something ?

Answer 1

Yes you can archive this using wildcard that needs to be configured on both, the dns server and http server
On the dns a entry like this (installing dns on ubuntu https://help.ubuntu.com/10.04/serverguide/C/dns.html):
; wildcard subdomains are all directed to this IP
; of course this should be the IP of your web server
*.domain.tld. IN A 1.2.3.4
At apache an entry like this:
<VirtualHost 111.22.33.55>
DocumentRoot /www/subdomain
ServerName www.domain.tld
ServerAlias *.domain.tld
</VirtualHost>
What happens after is that everything.domain.tld will be going to your main folder so you can use the index.php to redirect it to the right place or even an htaccess using mod_rewrite.