Sub-domain tangle (knotsmith required) - apache

Question

I seem to have painted myself into a corner with my plans for a series of website sub-domains. I wonder if my plans can be rescued or have I truly shot myself in the foot and would need to totally re-write a ton of stuff? Here's the problem:
I planned a series of sub-domain sites all dealing with variations on a theme. For illustrative purposes let's pretend I have the site www.colour.com (this is the 'hub' whose files reside in public_html) and then I add subdomains red.colour.com (in public_html/red), green.colour.com (in public_html/green) and blue.colour.com (in public_html/blue). Ok all good up to this point.
The thing is that these sites all share a lot of resources in common - style sheets, Javascripts, images etc. These are resources I don't want to replicate because it's a waste of space, but more importantly I don't want to risk developing different versions of files and them not all keeping in step with each other. So I did what I thought was the sane thing and I store all these at the 'hub' (in public_html/css, public_html/js etc).
What I discovered when my site went nearly live was that as soon as I defined e.g. public_html/red as red.colour.com, it could no longer 'see' any of it's supporting files that were located one level higher (in ../) and so the appearence and functionality broke down into a complete screen mess.
Short of a major re-write, is there any way out of this mess that anyone can think of?
Thanks in advance!
Frank.

Answer 1

I cracked it!
It required 1 pint of blood, 2 gallons of sweat and 3 magnums of tears, but I finally cracked it.
The secret is to use mod.rewrite as I was starting to suspect. You can indeed not address areas above the root, but there are other ways of refering to such locations, specifically you can refer to files or directories that 'don't exist' using the ReWrite conditions here:
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteCond %{SCRIPT_FILENAME} !-f
So for example, when you want to refer to the style sheet directory that was at a higher level than the currect context, you would refer to ../css, but after you've made the current context into it's own sub-domain, ../css no longer exists. That means you can make a match with one or both of the above rewrite conditions. Now it's just a case of pointng the client to the (e.g.) css directory via the original domain, www.colour.com/css, in my example. Here, for completeness, and to help any other poor soul from killing themselves over this (I had to learn regular expressions, mod.rewrite and Lord knows what else in 6 hours to solve this one! so I hope someone else benefits as well as me!)
DirectoryIndex index.php
Options +FollowSymLinks
RewriteEngine On
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteRule ^(.*)$ http://www.colours.com/$1 [R=301,L]
There may be some other directives worth adding such as to make it not rewrite hidden files, to prevent it looping etc but I haven't learn enough about mod.rewrite yet to make this squeeky clean. However it does work as it is and that is 99.99999% of my main goal.
Edit one week on.
Having lived with this solution a while I have to admit that there is a price to pay for this little bit of magic. I'm no expert as you will have gleaned, but it seems to me that this solution leads the browser to request each of the resources involved twice. This might not be a problem if your site is small and the efficiency hit unnoticeable, but if you want to be a stickler for optimum load times, then you might have to weigh up the pro's and con's of using this solution versus recoding your links into something more direct. Just so you know!

Answer 2

Frank, one slight tease: give us XYZ "then I can post a solution" isn't quite consistent with "every source including my web hosting company said it wasn't possible to do this".
Your approach is only sort doing what you want because a 301 redirect like this just passes the problem back to the client's browser telling it to refetch the resource from your other subdomain so it does two request for each resource -- which slows down the load time at the client.
Your first solution is that you could have done by just directly coding http://common.colour.com/... in your src and href attributes in your HTML. But this has the downside that you need to change your scripts. This approach is actually quite common as many high volume sites use a separate domain for such static resource and now often use a CDN for this. It can also have performance advantages as browsers will typically open two streams per domain for loading content but parallel up requests to separate streams.
Your second solution is to do this within your servers filesystem. What you need to do is to create symbolic links for DOCROOT/red/css to DOCROOT/css etc. If you are scripting in PHP you can do this by creating and executing a temporary configuration script in your DOCROOT and invoke it to add these links (which appear in your FTP browser as separate directory copies but in fact all point to shared resources. The key function that you need use is symlink() like this:
<?php
$root=dirname(__FILE__);
foreach( array( 'red', 'green', 'blue') as $c ){
foreach( array( 'css', 'js' ) as $d ) {
symlink( "$root/$c", "$root/$d/$c);
}
}
You'd need to tweak the colours and resource directories. Note that I've just typed this in and not debugged it -- costs extra ;-)
The third solution is to use an .htaccess file, but to do internal redirects rather than external ones. Here the Apache rewrite module maps the request directly to a different path/filename. I assume that your cpanel allows you to map XXX.colour.com to DOCROOT/xxx etc. so that a "GET /css/sheet.css" to a HTTP_HOST red.colour.com gets processed as DOCROOT/red/css/sheet.css. How you approach this depends on whether you use a single .htaccess at DOCROOT or separate red/.htaccess etc. If the former you can use a rule like:
RewriteEngine On
RewriteBase /
RewriteRule (red|green|blue)/(css|js|images)/(.*) /$2/$3 [L]
You do want the leading / on the rule target string here.
Try these out, and hope this helps :-)