Htaccess Rewrites are enabled by using the Apache module mod_rewrite, which is one of the most powerful Apache modules and features availale. Htaccess Rewrites through mod_rewrite provide the special ability to Rewrite requests internally as well as Redirect request externally.

When the url in your browser's location bar stays the same for a request it is an internal rewrite, when the url changes an external redirection is taking place. This is one of the first, and one of the biggest mental-blocks people have when learning about mod_rewrite... But I have a secret weapon for you to use, a new discovery from years of research that makes learning mod_rewrite drastically quicker and easier. It truly does or I wouldn't be saying so in the introduction of this article.

Despite the tons of examples and docs, mod_rewrite is voodoo. Damned cool voodoo, but still voodoo.
-- Brian Moore

Note: After years of fighting to learn my way through rewriting urls with mod_rewrite, I finally had a breakthrough and found a way to outsmart the difficulty of mod_rewrite that I just couldn't seem to master. The Mod_Rewrite RewriteCond/RewriteRule Variable Value Cheatsheet is the one-of-a-kind tool that changed the game for me and made mod_rewriting no-harder than anything else.

So keep that mod_rewrite reference bookmarked and you will be able to figure out any RewriteRule or RewriteCond, an amazing feat considering it took me a LONG time to figure this stuff out on my own. But that was before the craziness, one of the most challenging and productive .htaccess experiments I've done... An experiment so ILL it's sick like a diamond disease on your wrist! $$$. That mod_rewrite experiment/tutorial was the culmination of many different advanced mod_rewrite experiments I had done in the past and included most of my very best .htaccess tricks. With the cheatsheet it's no longer Voodoo.. Its just what you do. Now lets dig in!

If you really want to take a look, check out the mod_rewrite.c and mod_rewrite.h files.

Be aware that mod_rewrite (RewriteRule, RewriteBase, and RewriteCond) code is executed for each and every HTTP request that accesses a file in or below the directory where the code resides, so it's always good to limit the code to certain circumstances if readily identifiable.

For example, to limit the next 5 RewriteRules to only be applied to .html and .php files, you can use the following code, which tests if the url does not end in .html or .php and if it doesn't, it will skip the next 5 RewriteRules.

RewriteRule !\.(html|php)$ - [S=5]
RewriteRule ^.*-(vf12|vf13|vf5|vf35|vf1|vf10|vf33|vf8).+$ - [S=1]

.htaccess rewrite examples should begin with:

Options +FollowSymLinks
 
RewriteEngine On
RewriteBase /

Require the www

Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} !^www\.askapache\.com$ [NC]
RewriteRule ^(.*)$ http://www.askapache.com/$1 [R=301,L]

Loop Stopping Code

Sometimes your rewrites cause infinite loops, stop it with one of these rewrite code snippets.

RewriteCond %{REQUEST_URI} ^/(stats/|missing\.html|failed_auth\.html|error/).* [NC]
RewriteRule .* - [L]
 
RewriteCond %{ENV:REDIRECT_STATUS} 200
RewriteRule .* - [L]

Cache-Friendly File Names

This is probably my favorite, and I use it on every site I work on. It allows me to update my javascript and css files in my visitors cache's simply by naming them differently in the html, on the server they stay the same name. This rewrites all files for /zap/j/anything-anynumber.js to /zap/j/anything.js and /zap/c/anything-anynumber.css to /zap/c/anything.css

RewriteRule ^zap/(j|c)/([a-z]+)-([0-9]+)\.(js|css)$ /zap/$1/$2.$4 [L]

SEO friendly link for non-flash browsers

When you use flash on your site and you properly supply a link to download flash that shows up for non-flash aware browsers, it is nice to use a shortcut to keep your code clean and your external links to a minimum. This code allows me to link to site.com/getflash/ for non-flash aware browsers.

RewriteRule ^getflash/?$ http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=ShockwaveFlash [NC,L,R=307]

Removing the Query_String

On many sites, the page will be displayed for both page.html and page.html?anything=anything, which hurts your SEO with duplicate content. An easy way to fix this issue is to redirect external requests containing a query string to the same uri without the query_string.

RewriteCond %{THE_REQUEST} ^GET\ /.*\;.*\ HTTP/
RewriteCond %{QUERY_STRING} !^$
RewriteRule .* http://www.askapache.com%{REQUEST_URI}? [R=301,L]

Sending requests to a php script

This .htaccess rewrite example invisibly rewrites requests for all Adobe pdf files to be handled by /cgi-bin/pdf-script.php

RewriteRule ^(.+)\.pdf$  /cgi-bin/pdf-script.php?file=$1.pdf [L,NC,QSA]

Setting the language variable based on Client

For sites using multiviews or with multiple language capabilities, it is nice to be able to send the correct language automatically based on the clients preferred language.

RewriteCond %{HTTP:Accept-Language} ^.*(de|es|fr|it|ja|ru|en).*$ [NC]
RewriteRule ^(.*)$ - [env=prefer-language:%1]

Deny Access To Everyone Except PHP fopen

This allows access to all files by php fopen, but denies anyone else.

RewriteEngine On
RewriteBase /
RewriteCond %{THE_REQUEST} ^.+$ [NC]
RewriteRule .* - [F,L]

If you are looking for ways to block or deny specific requests/visitors, then you should definately read Blacklist with mod_rewrite. I give it a 10/10

Deny access to anything in a subfolder except php fopen

This can be very handy if you want to serve media files or special downloads but only through a php proxy script.

RewriteEngine On
RewriteBase /
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /([^/]+)/.*\ HTTP [NC]
RewriteRule .* - [F,L]

Require no www

Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} !^askapache\.com$ [NC]
RewriteRule ^(.*)$ http://askapache.com/$1 [R=301,L]

Check for a key in QUERY_STRING

Uses a RewriteCond Directive to check QUERY_STRING for passkey, if it doesn't find it it redirects all requests for anything in the /logged-in/ directory to the /login.php script.

RewriteEngine On
RewriteBase /
RewriteCond %{QUERY_STRING} !passkey
RewriteRule ^/logged-in/(.*)$ /login.php [L]

Removes the QUERY_STRING from the URL

If the QUERY_STRING has any value at all besides blank than the?at the end of /login.php? tells mod_rewrite to remove the QUERY_STRING from login.php and redirect.

RewriteEngine On
RewriteBase /
RewriteCond %{QUERY_STRING} .
RewriteRule ^login.php /login.php? [L]

Fix for infinite loops

An error message related to this isRequest exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace.or you may seeRequest exceeded the limit,probable configuration error,Use 'LogLevel debug' to get a backtrace, orUse 'LimitInternalRecursion' to increase the limit if necessary

RewriteCond %{ENV:REDIRECT_STATUS} 200
RewriteRule .* - [L]

External Redirect .php files to .html files (SEO friendly)

RewriteRule ^(.*)\.php$ /$1.html [R=301,L]

Internal Redirect .php files to .html files (SEO friendly)

Redirects all files that end in .html to be served from filename.php so it looks like all your pages are .html but really they are .php

RewriteRule ^(.*)\.html$ $1.php [R=301,L]

block access to files during certain hours of the day

Options +FollowSymLinks
RewriteEngine On
RewriteBase /
# If the hour is 16 (4 PM) Then deny all access
RewriteCond %{TIME_HOUR} ^16$
RewriteRule ^.*$ - [F,L]

Rewrite underscores to hyphens for SEO URL

Converts all underscores "_" in urls to hyphens "-" for SEO benefits... See the full article for more info.

Options +FollowSymLinks
RewriteEngine On
RewriteBase /
 
RewriteRule !\.(html|php)$ - [S=4]
RewriteRule ^([^_]*)_([^_]*)_([^_]*)_([^_]*)_(.*)$ $1-$2-$3-$4-$5 [E=uscor:Yes]
RewriteRule ^([^_]*)_([^_]*)_([^_]*)_(.*)$ $1-$2-$3-$4 [E=uscor:Yes]
RewriteRule ^([^_]*)_([^_]*)_(.*)$ $1-$2-$3 [E=uscor:Yes]
RewriteRule ^([^_]*)_(.*)$ $1-$2 [E=uscor:Yes]
 
RewriteCond %{ENV:uscor} ^Yes$
RewriteRule (.*) http://d.com/$1 [R=301,L]

Require the www without hardcoding

Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} !^www\.[a-z-]+\.[a-z]{2,6} [NC]
RewriteCond %{HTTP_HOST} ([a-z-]+\.[a-z]{2,6})$     [NC]
RewriteRule ^/(.*)$ http://%1/$1 [R=301,L]

Require no subdomain

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} \.([a-z-]+\.[a-z]{2,6})$ [NC]
RewriteRule ^/(.*)$ http://%1/$1 [R=301,L]

Require no subdomain

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} \.([^\.]+\.[^\.0-9]+)$
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]

Redirecting WordPress Feeds to Feedburner

Full article:Redirecting WordPress Feeds to Feedburner

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_URI} ^/feed\.gif$
RewriteRule .* - [L]
 
RewriteCond %{HTTP_USER_AGENT} !^.*(FeedBurner|FeedValidator) [NC]
RewriteRule ^feed/?.*$ http://feeds.feedburner.com/apache/htaccess [L,R=302]
 
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

Only allow GET and PUT Request Methods

Article: Request Methods

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_METHOD} !^(GET|PUT)
RewriteRule .* - [F]

Prevent Files image/file hotlinking and bandwidth stealing

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?askapache.com/.*$ [NC]
RewriteRule \.(gif|jpg|swf|flv|png)$ /feed/ [R=302,L]

Stop browser prefetching

RewriteEngine On
SetEnvIfNoCase X-Forwarded-For .+ proxy=yes
SetEnvIfNoCase X-moz prefetch no_access=yes
 
# block pre-fetch requests with X-moz headers
RewriteCond %{ENV:no_access} yes
RewriteRule .* - [F,L]

This module uses a rule-based rewriting engine (based on a regular-expression parser) to rewrite requested URLs on the fly. It supports an unlimited number of rules and an unlimited number of attached rule conditions for each rule, to provide a really flexible and powerful URL manipulation mechanism. The URL manipulations can depend on various tests, of server variables, environment variables, HTTP headers, or time stamps. Even external database lookups in various formats can be used to achieve highly granular URL matching.

This module operates on the full URLs (including the path-info part) both in per-server context (httpd.conf) and per-directory context (.htaccess) and can generate query-string parts on result. The rewritten result can lead to internal sub-processing, external request redirection or even to an internal proxy throughput.

Further details, discussion, and examples, are provided in the detailed mod_rewrite documentation.

Directives

• RewriteBase
• RewriteCond
• RewriteEngine
• RewriteLock
• RewriteLog
• RewriteLogLevel
• RewriteMap
• RewriteOptions
• RewriteRule

If you aren't already comfortable using mod_rewrite then I recommend this excellent mod_rewrite guide by one of my favorite mod_rewrite gurus that I've met.

htaccess Guide Sections

• htaccess tricks for Webmasters
• HTTP Header control with htaccess
• PHP on Apache tips and tricks
• SEO Redirects without mod_rewrite
• mod_rewrite examples, tips, and tricks
• HTTP Caching and Site Speedups
• Authentication on Apache
• htaccess Security Tricks and Tips
• SSL tips and examples
• Variable Fun (mod_env) Section
• .htaccess Security with MOD_SECURITY
• SetEnvIf and SetEnvIfNoCase Examples

« Search Engine Friendly Redirects | .htaccess Tutorial Index | » Speed up your site with Caching and cache-control

Htaccess Rewrites – Rewrite Tricks and Tips originally appeared on AskApache.com

Bayonetta: In For the Kill Extended Trailer

Nice example of chaotic beats, but they make melody somehow, it's rather an addictive beat.

What random chaos have I spent the last 6 months on? Experiments with DNS, Fail-over technology for MySQL/DNS/WWW/MAIL servers for free or for very cheap, chrooting servers and of course testing new security idea.... But the exciting stuff for me personally is some very cool ways to make sure you are never unable to remotely access your server in case of catastrophic failure.. That's what it's all about for me you know, making things work so well that they run themselves and free up time for life! I'm around a 1/4 of a century old.. I'm done playing around, it's time to make some cash before they put me in an old-folks home.. My time is short, my cause is just.. We will prevail! lol.. I'm 25 and I still got jokes!

For 2010 I have a few choice articles and ideas I'm debating about publishing.. I don't want to give the wrong kind of people power, I want to give the power to the people -- but at a certain point it takes a serious investment to actually empower yourself, whereas a company could afford to actually bring it to reality.. So who does the knowledge benefit then? No, the only way is to get serious myself and beat the profiteers to the punch so to offer a service that would be dirt-cheap if it weren't in the hands of gluttons.

I've been pursuing research into several new areas of web technology (no not a smartphone app!) over the past year trying to increase my business profits and quailty of service, and I am becoming more aware every day that I can do it better and cheaper! Any industry always has those at the top who enjoy knowing things that keep them on top, and try to prevent others from doing what they did.. It's not like the information is so wizard-like that it's just not possible for average folks to comprehend.. It's just only discussed behind closed doors, masked in schools by tenure and a defined curriculum. But since this is the Wild Wild Web the barriers can always be circumvented. Stick around, I am already looking for partners (both investors and linux/code kungfu masters).

Enjoy the jam session ;)

Bayonetta Trailer originally appeared on AskApache.com

My traffic is growing, alot, and I need to plan how I'm going to maintain scalability, high availability, and redundancy. Scalability is an application's ability to support a growing number of users. High availability can be defined as redundancy or speed. I decided to setup Round Robin DNS for static.askapache.com, which is the "static" subdomain of AskApache that serves all the static assets like images, javascript, css, etc.. (BTW, the z stands for ZAP).. All I needed to attempt setting this up was another hosting account on a separate server. I have hosting accounts with around 10 different companies from working with various clients over the years, like Powweb and I don't use them because they suck in terms of the unix environment. Many of these web hosts are actually very fast bandwidth-wise..

Round Robin Concept

A few months ago I was given a free hosting account on HostGator to evaluate and tempt me away from DreamHost to become a Gator. I get a lot of these types of offers from time to time from the smaller Web companies who read AskApache.. but when I noticed the SSH access was jailed and saw how restrictive the shell was I felt like I was on a windows box.. I want a shell, cpanel sucks. I compile and run everything from the shell so thats was a deal-breaker and I sorta forgot all about it.

The goal is to add the HostGator server to be an exact mirror of the static.askapache.com domain, then to add that server as a 2nd A record to my DNS zone. That way half the visitors to the size will be taking up resources and bandwidth on the HostGator server instead of mine.

Round Robin A records in DNS are intended to evenly distribute queries between each host of the same name. Using some tricks straight out of a hackers toolbox we can verify if the distribution is taking place. (It is.)

DNS - Domain Name System

The Domain Name System is often analogized as a "phone book" for the Internet because it translates human-friendly computer hostnames into IP addresses. For example, www.askapache.com translates to 208.113.134.190. Every request for a human-friendly hostname first needs to be translated to the IP before the server can be queried. Normally each hostname corresponds to exactly 1 IP address. But in a Round Robin setup, the idea is to have the hostname correspond to multiple IP addresses, which are different servers that house the exact same content, resulting in some hosts requesting files from one server, and another host requesting files from the other server, resulting in less CPU resources and bandwidth.

Here is an the zone for static.askapache.com Round Robin records:

Round Robin DNS

Round robin DNS is a technique of load distribution, load balancing, or fault-tolerance provisioning multiple, redundant Internet Protocol service hosts, e.g., Web servers, FTP servers, by managing the Domain Name System's (DNS) responses to address requests from client computers according to an appropriate statistical model.

In its simplest implementation Round-robin DNS works by responding to DNS requests not only with a single IP address, but a list of IP addresses of several servers that host identical services. The order in which IP addresses from the list are returned is the basis for the term round robin. With each DNS response, the IP address sequence in the list is permuted. Usually, basic IP clients attempt connections with the first address returned from a DNS query so that on different connection attempts clients would receive service from different providers, thus distributing the overall load among servers.

Round robin DNS is often used for balancing the load of geographically-distributed Web servers. For example, a company has one domain name and three identical web sites residing on three servers with three different IP addresses. When one user accesses the home page it will be sent to the first IP address. The second user who accesses the home page will be sent to the next IP address, and the third user will be sent to the third IP address. In each case, once the IP address is given out, it goes to the end of the list. The fourth user, therefore, will be sent to the first IP address, and so forth.

Although easy to implement, round robin DNS has problematic drawbacks, such as those arising from record caching in the DNS hierarchy itself, as well as client-side address caching and reuse, the combination of which can be difficult to manage. Round robin DNS should not solely be relied upon for service availability. If a service at one of the addresses in the list fails, the DNS will continue to hand out that address and clients will still attempt to reach the inoperable service.

Does Round Robin Work

Definately. I can look at the access logs for both servers and see that they are splitting the requests nicely. It is definately not an exact split however, look at these statistics and you'll see what I mean.

$ dig @ns1.dreamhost.com +authority +all static.askapache.com
 
;; ANSWER SECTION:
static.askapache.com.        14400   IN      A       69.56.174.114
static.askapache.com.        14400   IN      A       64.111.114.111
 
$ dig @ns1.dreamhost.com +authority +all static.askapache.com
 
;; ANSWER SECTION:
static.askapache.com.        14400   IN      A       64.111.114.111
static.askapache.com.        14400   IN      A       69.56.174.114

The effects of caching will distort the effectiveness of any IP address allocation algorithm unless a 0 TTL is used which has the effect of significantly increasing the load on the DNS (and is not always implemented consistently). In this case the cure may be worse than the disease Good news we have good load balancing on our web servers. Bad news we need 17 more DNS servers!. Intuitively, and without running any experiments to verify, we would suggest that given a normal TTL (12 hours or more) and ANY IP allocation algorithm other than a single static list, loads should be reasonably balanced .

Full root server query

Tracing to static.askapache.com[a] via A.ROOT-SERVERS.NET, maximum of 3 retries
A.ROOT-SERVERS.NET [.] (198.41.0.4)
 |\___ L.GTLD-SERVERS.NET [com] (192.41.162.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ D.GTLD-SERVERS.NET [com] (192.31.80.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ J.GTLD-SERVERS.NET [com] (192.48.79.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ H.GTLD-SERVERS.NET [com] (192.54.112.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ E.GTLD-SERVERS.NET [com] (192.12.94.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ F.GTLD-SERVERS.NET [com] (192.35.51.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ I.GTLD-SERVERS.NET [com] (192.43.172.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ G.GTLD-SERVERS.NET [com] (192.42.93.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ B.GTLD-SERVERS.NET [com] (2001:0503:231d:0000:0000:0000:0002:0030) Not queried
 |\___ B.GTLD-SERVERS.NET [com] (192.33.14.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ A.GTLD-SERVERS.NET [com] (2001:0503:a83e:0000:0000:0000:0002:0030) Not queried
 |\___ A.GTLD-SERVERS.NET [com] (192.5.6.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ C.GTLD-SERVERS.NET [com] (192.26.92.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 |\___ M.GTLD-SERVERS.NET [com] (192.55.83.30)
 |     |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
 |     |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
 |      \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
  \___ K.GTLD-SERVERS.NET [com] (192.52.178.30)
       |\___ ns3.dreamhost.com [askapache.com] (66.33.216.216) Got authoritative answer
       |\___ ns2.dreamhost.com [askapache.com] (208.96.10.221)
        \___ ns1.dreamhost.com [askapache.com] (66.33.206.206) Got authoritative answer
 
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 64.111.114.111
  ns1.dreamhost.com (66.33.206.206)       static.askapache.com -> 69.56.174.114
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 64.111.114.111
  ns3.dreamhost.com (66.33.216.216)       static.askapache.com -> 69.56.174.114

Live Online DNS Tools

• DNSstuff.com - Your Destination for DNS and Networking Tools
• ZoneCheck
• Quick Check - Pingability.com
• Squishywishywoo: complete dns traversal checking
• ZoneCut DNS
• DNS Sleuth
• DNS test - Domain name DNS test - pweb.cz
• OpenDNS - Support - CacheCheck
• DNSReport
• DNSTrace
• intoDNS
• DNSthru.com
• DNS Doctor
• Power Check

More Reading

• HOWTO - Configure Load Balancing
• Load Sharing with DNS

RFC's related to DNS

• RFC 920: Specified original TLDs: .arpa, .com, .edu, .org, .gov, .mil and two-character country codes
• RFC 1032: Domain administrators guide
• RFC 1033: Domain administrators operations guide
• RFC 1034: Domain Names - Concepts and Facilities.
• RFC 1035: Domain Names - Implementation and Specification
• RFC 1101: DNS Encodings of Network Names and Other Types
• RFC 1123: Requirements for Internet Hosts -- Application and Support
• RFC 1912: Common DNS Operational and Configuration Errors
• RFC 1995: Incremental Zone Transfer in DNS
• RFC 1996: A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)
• RFC 2136: Dynamic Updates in the domain name system (DNS UPDATE)
• RFC 2181: Clarifications to the DNS Specification
• RFC 2182: Selection and Operation of Secondary DNS Servers
• RFC 2308: Negative Caching of DNS Queries (DNS NCACHE)
• RFC 2317: Classless IN-ADDR.ARPA delegation
• RFC 2671: Extension Mechanisms for DNS (EDNS0)
• RFC 3597: Handling of Unknown DNS Resource Record (RR) Types
• RFC 3696: Application Techniques for Checking and Transformation of Names
• RFC 4343: Domain Name System (DNS) Case Insensitivity Clarification
• RFC 4592: The Role of Wildcards in the Domain Name System
• RFC 4892: Requirements for a Mechanism Identifying a Name Server Instance
• RFC 5001: DNS Name Server Identifier Option (NSID)
• RFC 5395: Domain Name System (DNS) IANA Considerations

This page contains content by Author of Article from Wikipedia and is licensed under the GNU FDL.

Table of Contents

• Round Robin Concept
• DNS - Domain Name System
• Round Robin DNS
• Efficacy of DNS Load Balancing
• Live Online DNS Tools
• More Reading
• RFC's related to DNS

DNS Round Robin Configuration using Rsync over SSH originally appeared on AskApache.com

mod_rewrite is very useful in many situations. Yet some behaviors were not so obvious when I started to mess with it. After many testings, I understand it much better, now. Having said that, I do not pretend to know it perfectly. I also make mistakes.

So, although I tested all these on my local server and PowWeb, do not trust what I say blindly. Rather, please use it as a suggestion or bases for your own experiments.

First thing

# You need this in your .htaccess on some servers.
# You don't need it on PowWeb because it's already set.
 
# You must put this line '''once''' before to put RewrteRule.
 
# You don't have to put this in many cases.
# But specifying it can reduce the risk of endless looping.
#
# Also, certain internal redirect rules and conditions
# will not work well if you don't use this line.
# So, put it, and forget about adding / at the beginning of the
# substitute string
 
# With "RewriteBase /",  substitute string of RewriteRule will have
# forward slash added automatically.
#
# But this have no effect on %{REQUEST_URI}, and it starts with
# forward slash unlike URL of RewriteRule.
#
# RewriteRule URL: "/" is stripped automatically.
# RewriteRule substitute: "/" is added automatically.
# %(REQUEST_URI}: always start with "/".
 
# RewriteRule have following format.
# Each part separated by a space.
 
# REGEX  is Perl compatible Regular expression.
 
# ex. RewriteRule ^(abc.*)$ xxx$1 [R]
#
#  ^ == beginning of URL
#  $ == end of URL
#  . (period) == matches any one character
#  * == matches with zero or more of previous character.
#
#  The URL is matched against REGEX without "http://host.com/",
#  and the QUERY_STRING part (the part after ? ) stripped.
#  ie. The address: http://zoro.com
'''/faint.cgi'''?a=2&b=xxx
#  The URL used in the rule: '''/faint.cgi'''
#
#  So, this matches any URL starting with "abc".
#  And entire URL is grouped by ( ) to be used in the substitution
#  (referenced by) $1.
#  As an option, this specify external redirect 302 (Temorary)
 
# RewriteRules may have additional Conditions.
 
RewriteCond STRING expression [optional flags]
RewriteRule REGEX substitution [optional flags]

RewriteRule ^xxx/(.*)$ yyy/$1

RewriteRule ^(.*)\.html xyz/whatever.cgi?$1  [L]

RewriteRule ^ - [L]

RewriteRule ^(.*)/abc\.html$ abc/$1 [L]
RewriteRule ^(.*)$ xyz/$1 [L]

RewriteRule ^(.*)$ xyz/$1

RewriteRule ^(.*)$ xyz/$1

RewriteRule ^(.*)$ index.php?p=$1

RewriteRule b.html a.html

RewriteCond %{THE_REQUEST} ^(GET|HEAD)\ /b.html
RewriteRule b.html a.html

RewriteCond %{QUERY_STRING} __XXX__$
RewriteRule /$ - [L]
RewriteCond %{QUERY_STRING} ^(.*)__XXX__$
RewriteRule ^(.*)$ $1?%1 [L]
 
# Add key string to the QUERY_STRING
RewriteRule ^(.*)$ $1?%{QUERY_STRING}__XXX__
 
# Following rules will be checked only onece,
# as long as QUERY_STRING is unmodified or the key string is kept.
 
# No modification to the QUERY_STRING
RewriteRule ^(other.*)$ rules/$1
 
# QUERY_STRING is conserved
RewriteRule ^(more.*)$ rules.cgi?$1%{QUERY_STRING}
 
# key string is placed, explicitly.
RewriteRule ^(yetmore.*)$ rules.cgi?$1__XXX___
 
I tried to use [E=ENVVAR:STRING] to distinguish the subsequest round but ENV
variables seem to be reset on each round... So, following example for preventing 2nd round does not work.
 
RewriteRule ^.*$ - [L]
 
RewriteRule ^.*$ - [L,E=DONE:YES]

RewriteRule ^pattern1$ substitute1
RewriteRule ^pattern2$ substitute2
RewriteRule ^pattern3$ substitute3
 
RewriteCond %{ENV:DONE} YES
RewriteRule ^patternX$ substituteX

# As this is not usually available to CGI program,
# it is very useful in DIY authentication with CGI.
RewriteRule ^.*$ - [E=HTTP_AUTH:%{HTTP:Authorization}]
 
# available in RewriteRules.
RewriteRule ^.*$ - [E=HTTP_TIME:%{TIME}]
 
QUERY_STRING can be used for passing parameters, too.
 
RewriteRule ^(.*)$ $1?AUTH=%{HTTP:Authorization} [QSA]

RewriteRule ^(.*)$ subdir/$1
 
# This is not efficient...and may not work sometime
# because the REQUEST_URI may contain "subdir/"
# in a part of QUERY_STRING, and also it matches
# "/sub/sub-subdir" and "/abcdefgsubdir/" and so on.
 
RewriteRule ^(.*)$ subdir/$1

RewriteEngine on
RewriteBase /
 
RewriteRule ^blank\.txt - [L]
 
RewriteCond %{HTTP_USER_AGENT}
 (MSIECrawler|Ninja|Microsoft|MSFront|WebCopier|Pockey) [NC]
RewriteRule ^(.*)$  blank.txt [L]

RewriteRule ^/*(([^/]+)/+([^/]+)/+([^/]+)/*(.*)$ index.php?$1=$2&$3=$4 [L]

RewriteRule ^/*([^/]+)/+([^/]+)(.*)/*$ $3?$1=$2 [L,QSA]
RewriteRule ^([^/]+)$ index.php?$1 [L,QSA]

RewriteRule ^/*([^/]+)/+([^/]+)/+([^/]+)/+([^/]+)(.*)/*$ $5?$1=$2&$3=$4 [L,QSA]
RewriteRule ^([^/]+)$ index.php?$1 [L,QSA]

RewriteRule ^/*(([^/]+)/+([^/]+)/*(.*)$ index.php?aa=$1&bb=$2&$3 [L]

RewriteRule ^([^&]*)&(.*)$ $1\%26$2 [NE,N]
RewriteRule ^([^&]*)$ whatever.php?title=$1 [L]

Mod_Rewrite Basic Examples originally appeared on AskApache.com