How to limit mod_rewrite to a single directory?

Apache mod_rewrite RewriteRule question

• Apache RewriteRule to redirect Get requests to another server based on file suffix. I would like to set up a quick and dirty content load sharing scheme using mod_rewrite on Apache 1.3. The objective is to have large media files (.pdf, .avi, .mpeg, etc.) transparently served from a secondary server via URL rewriting. The goal is to preserve performance and conserve bandwidth on the primary web server during heavy download periods. I believe the httpd.conf syntax would look something like this: RewriteEngine on RewriteRule source_url redirect_url [R,L] Where: source_url has the form: http://www.example.com/content/bigfile.mpeg redirect_url has the form: http://secondary.example.com/content/bigfile.mpeg If so, I need help with the regular expression for the RewriteRule that maps the 1st URL to the 2nd URL. I'm looking for a regular expression that, for a defined list of file types, redirects requests for those files from http://www.example.com/* to http://secondary.example.com/* Related questions: 1) Is this a sound approach to splitting load across multiple servers? 2) Does it matter whether the context for the RewriteRule is at the VirtualHost or the Directory level? 3) Can this approach be extended to cheap and cheerul load balancing via mod_rewrite where rather than redirecting traffic based on a rule to a single host, the redirection can happen to one of a list of hosts on a random or round robin basis? TIA! Brian

• Answer:

  Hi, Brian. Thanks for your question. You can achieve what you want using the following rule: RewriteEngine on RewriteRule ^(.*)/([^/]*\.)(avi|pdf|mpeg)$ http://secondary.example.com/%241/%242%243 [R,L] (The RewriteRule line should not have any line breaks, if Google has inserted any). This will redirect any requests that end in '.avi', '.pdf', or '.mpeg' to the matching address on http://secondary.example.com/. If you need to add more file types, add a bar and the type after '|mpeg'. secondary.example.com can be replaced with your server's hostname. As an example, if I wanted to also redirect files ending in '.bla' and '.pie' to a server 'files.test.com', the line would become: RewriteRule ^(.*)/([^/]*\.)(avi|pdf|mpeg|bla|pie)$ http://files.test.com/%241/%242%243 [R,L] To answer your questions: 1. This is a fairly good way to serve files of specific types from a different server, especially if bandwidth is the problem. However, too many requests for large media files will just move the problem of load onto the second server. If this is acceptable (for example, if you wish to ensure your primary web server remains accessable), then this method should work well. It is also worth noting that enabling mod_rewrite will slow down server performance a little, especially if it is applied site-wide. The effects should be negligible, though. 2. Functionally, it does not matter whether this is included in the VirtualHost directive, or in a .htaccess file. However, bear in mind that if it is included in such a way as to apply to every request, server performance may suffer unnecessarily. A better approach may be to use it in a .htaccess file only in the directory with media - '/content/', in your example. Note that if you did this, you would probably have to change http://secondary.example.com/%241/%242%243 in the example above to http://secondary.example.com/content/%241/%242%243. 3. Yes, mod_rewrite is flexable enough to allow this. To do this, you would need to create a text file containing a list of possibile servers, for example: mediaservers files1|files2|files3|... You would then need to add the following directive before the RewriteRule: RewriteMap servers rnd:/path/to/your/server/list.txt And finally, modify the rule to something similar to: RewriteRule ^(.*)/([^/]*\.)(avi|pdf|mpeg)$ http://${servers:mediaservers}.example.com/$1/$2$3 [R,L] This would select one of the servers listed in your text file at random, effectively spreading the load between them. This isn't the best solution, since it would not take into account, for example, a server less able to cope with load than others. For more information, see: http://apache.active-venture.com/mod/mod_rewrite2.html#RewriteMap This isn't really what mod_rewrite was designed for though, so the performance probably won't be as good as that of a dedicated load balancer, or software designed to balance loads. A better software solution may be pound (http://www.apsis.ch/pound/), Pure Load Balancer (http://plb.sunsite.dk/) or Zeus Load Balancer (http://www.zeus.com/products/zlb/), as a few examples. The apache module mod_backhand (http://www.backhand.org/mod_backhand/) may also be useful if the problem is CPU usage. It does not help with bandwidth utilisation, though. I hope this helps. If you have any questions, please do not hesitate to request a clarification. The following links may also be of use to you: Apache URL Rewriting Guide: http://httpd.apache.org/docs/misc/rewriteguide.html Load balancing using mod_rewrite and mod_proxy: http://wiki.apache.org/cocoon/LoadBalancingWithModProxy The pound load balancer: http://www.apsis.ch/pound/ Regular Expressions Reference: http://www.zvon.org/other/reReference/Output/ The following searches may also be useful: 'mod_rewrite load balancing': ://www.google.com/search?q=mod_rewrite+load+balancing --wildeeo