URL/Subdomain rewrites (htaccess) - .htaccess

Question

Say I have the following file:
http://www.example.com/images/folder/image.jpg
I want to serve it on
http://s1.example.com/folder/image.jpg
How can I do a htaccess rewrite to point it to it?
Like for example, I make a subdomain s1.example.com and then on that subdomain, I add a htaccess rule to point any files, to pull it from http://www.example.com/images/
Does serving files this way act as serving content from a cookieless domain?

Answer 1

First let me talk a bit about the concept of cookieless domains. Normally, when requesting anything over http, any relevant cookies are sent with the request. Cookies, are dependent on which domain they come from. The idea of using a cookieless domain is that you relocate static content that doesn't cookies, like images, to a separate domain so that no cookies will be sent with that request. This cuts out a small amount of traffic.
How much you gain from doing this depends on the type of page. The more images you have, the more you gain. If your site loads a big bunch of small images, such as avatars or image thumbnails, you might have a lot to gain. On the contrary, if your site doesn't use any cookies, you have nothing to gain. It's entirely possible that your page won't load noticeably faster, if it only uses a small amount of images, which will be cached between page loads anyway.
One thing to keep in mind, too, is that cookies set for example.com will also be sent with requests to s1.example.com as "s1." is a subdomain to example.com. You need to use www. (or any other subdomain of your choice) in order to separate the cookie spaces.
Secondly, if you decide that a cookieless domain is actually something worth trying, let's talk about the implementation.
Shikhar's solution is bad! While the solution appears to work on the surface, it actually defeats the purpose of using a cookieless domain. For every image, first the s1. url is tried. The s1. URL then makes a redirect to the www. domain which triggers a second http request. This is a loss, no matter how you look at it. What you need is a rewrite, which changes the URL internally on the web server, without the browser even realizing.
For simplicity, I'm assuming that all domains point to the same directory, so that www.example.com/something = example.com/something = s1.example.com/something = blub.example.com/something. This makes things simpler if you really need store the images physically in "www.example.com/images".
I'd recommend a .htaccess that looks a little something like this:
# Turn on rewrites
RewriteEngine On
# Rewrite all requests for images from s1, so they are fetched from the right place
RewriteCond %{HTTP_HOST} ^s1\.example\.com
# Prevent an endless loop from ever happening
RewriteCond %{REQUEST_URI} !^/images
RewriteRule (.+) /images/$1 [L]
# Redirect http://s1.example.com/ to the main page (in case a user tries it)
RewriteCond %{HTTP_HOST} ^s1\.example\.com
RewriteRule ^$ http://www.example.com/ [R=301,L]
# Redirect all requests with other subdomains, or without a subdomain to www.
# Eg, blub.example.com/something -> www.example.com/something
# example.com/something -> www.example.com/something
RewriteCond %{HTTP_HOST} !^www\.example\.com
RewriteCond %{HTTP_HOST} !^s1\.example\.com
RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]
# Place any additional rewrites below.

Answer 2

Just for people's general info who like me may be investigating the benefits of this. From what I'm reading it isn't just cutting down on the upstream overhead of eliminating cookies sent with http requests. Apparently many browsers limit max connections to 1 domain/server to 6 concurrent. So if you have a separate domain on a diff server you get to double that to 12. Which to me would seem like the main potential here for a serious speed boost.
Though anyway, if I'm understanding this correctly. The other domain serving the static content needs to be located on another server from the main domain. Actually makes sense, avid firefox user and tweaker. When you check the about:config settings in firefox the max connections per server is set to 6 by default. A person can manually bump it up to a max of 8. But most firefox users probably don't spend enough time getting familiar with how to modify the browser and leave it to the default max of 6.
Not sure how many the other browsers set by default and then there is older browser versions that are still in use to consider. Bottomline ... makes perfect sense that enabling the browser to double the total number of connections using two servers would have to be a loadtime improvement. Using a sub-domain on the same server a person isn't going to be able to take advantage of that.

Answer 3

If you mean to redirect the traffic from www.example.com to s1.example.com, use the following htaccess on www.example.com
RewriteCond %{HTTP_HOST} ^(s1\.example\.com)
RewriteRule (.*) http://www.example.com%{REQUEST_URI}[R=301,NC,L]
If this is not what you are looking for, elaborate the question further.

Answer 4

I think you may have it backwards, (or very possibly I do). To clarify, if you're implementing a cookie-less subdomain & have a base URL of www. at least in this case, cookies are set on www, for example: a major cookie setter is google analytics, so when setting their script on my site it looks like this:
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'analytics-acc-#],
['_setDomainName', '[www.valpocreative.com][1]'],
['_trackPageview']);
You can see here that I set my main domain to www, correct me if i'm wrong in my case I would need to redirect www to non www subdomain & not the other way around. This is also the cname setup made on my cpanel (cname= "cdn" pointing to www.domain.com)