From fe39ffb8b90ae4e002ed73fe98617cd590abb467 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 27 Apr 2024 08:33:50 +0200 Subject: Adding upstream version 2.4.56. Signed-off-by: Daniel Baumann --- docs/manual/rewrite/advanced.html.en | 370 +++++++++++++++++++++++++++++++++++ 1 file changed, 370 insertions(+) create mode 100644 docs/manual/rewrite/advanced.html.en (limited to 'docs/manual/rewrite/advanced.html.en') diff --git a/docs/manual/rewrite/advanced.html.en b/docs/manual/rewrite/advanced.html.en new file mode 100644 index 0000000..c2ad1c0 --- /dev/null +++ b/docs/manual/rewrite/advanced.html.en @@ -0,0 +1,370 @@ + + + + + +Advanced Techniques with mod_rewrite - Apache HTTP Server Version 2.4 + + + + + + +
+

Modules | Directives | FAQ | Glossary | Sitemap

+

Apache HTTP Server Version 2.4

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+
<-
+

Advanced Techniques with mod_rewrite

+
+

Available Languages:  en  | + fr 

+
+ + +

This document supplements the mod_rewrite +reference documentation. It provides +a few advanced techniques using mod_rewrite.

+ +
Note that many of these examples won't work unchanged in your +particular server configuration, so it's important that you understand +them, rather than merely cutting and pasting the examples into your +configuration.
+ +
+ +
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+
+

URL-based sharding across multiple backends

+ + + +
+
Description:
+ +
+

A common technique for distributing the burden of + server load or storage space is called "sharding". + When using this method, a front-end server will use the + url to consistently "shard" users or objects to separate + backend servers.

+
+ +
Solution:
+ +
+

A mapping is maintained, from users to target servers, in + external map files. They look like:

+ +

+user1 physical_host_of_user1
+user2 physical_host_of_user2
+# ... and so on +

+ +

We put this into a map.users-to-hosts file. The + aim is to map;

+ +

+/u/user1/anypath +

+ +

to

+ +

+http://physical_host_of_user1/u/user/anypath +

+ +

thus every URL path need not be valid on every backend physical + host. The following ruleset does this for us with the help of the map + files assuming that server0 is a default server which will be used if + a user has no entry in the map:

+ +
RewriteEngine on
+RewriteMap    users-to-hosts      "txt:/path/to/map.users-to-hosts"
+RewriteRule   "^/u/([^/]+)/?(.*)" "http://${users-to-hosts:$1|server0}/u/$1/$2"
+ +
+
+ +

See the RewriteMap + documentation and the RewriteMap HowTo + for more discussion of the syntax of this directive.

+ +
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+
+

On-the-fly Content-Regeneration

+ + + +
+
Description:
+ +
+

We wish to dynamically generate content, but store it + statically once it is generated. This rule will check for the + existence of the static file, and if it's not there, generate + it. The static files can be removed periodically, if desired (say, + via cron) and will be regenerated on demand.

+
+ +
Solution:
+ +
+ This is done via the following ruleset: + +
# This example is valid in per-directory context only
+RewriteCond "%{REQUEST_URI}"   "!-U"
+RewriteRule "^(.+)\.html$"     "/regenerate_page.cgi"   [PT,L]
+ + +

The -U operator determines whether the test string + (in this case, REQUEST_URI) is a valid URL. It does + this via a subrequest. In the event that this subrequest fails - + that is, the requested resource doesn't exist - this rule invokes + the CGI program /regenerate_page.cgi, which generates + the requested resource and saves it into the document directory, so + that the next time it is requested, a static copy can be served.

+ +

In this way, documents that are infrequently updated can be served in + static form. if documents need to be refreshed, they can be deleted + from the document directory, and they will then be regenerated the + next time they are requested.

+
+
+ +
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+
+

Load Balancing

+ + + +
+
Description:
+ +
+

We wish to randomly distribute load across several servers + using mod_rewrite.

+
+ +
Solution:
+ +
+

We'll use RewriteMap and a list of servers + to accomplish this.

+ +
RewriteEngine on
+RewriteMap lb        "rnd:/path/to/serverlist.txt"
+RewriteRule "^/(.*)" "http://${lb:servers}/$1"     [P,L]
+ + +

serverlist.txt will contain a list of the servers:

+ +

+## serverlist.txt
+
+servers one.example.com|two.example.com|three.example.com
+

+ +

If you want one particular server to get more of the load than the +others, add it more times to the list.

+ +
+ +
Discussion
+
+

Apache comes with a load-balancing module - +mod_proxy_balancer - which is far more flexible and +featureful than anything you can cobble together using mod_rewrite.

+
+
+ +
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+
+

Structured Userdirs

+ + + +
+
Description:
+ +
+

Some sites with thousands of users use a + structured homedir layout, i.e. each homedir is in a + subdirectory which begins (for instance) with the first + character of the username. So, /~larry/anypath + is /home/l/larry/public_html/anypath + while /~waldo/anypath is + /home/w/waldo/public_html/anypath.

+
+ +
Solution:
+ +
+

We use the following ruleset to expand the tilde URLs + into the above layout.

+ +
RewriteEngine on
+RewriteRule   "^/~(([a-z])[a-z0-9]+)(.*)"  "/home/$2/$1/public_html$3"
+ +
+
+ +
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+
+

Redirecting Anchors

+ + + +
+
Description:
+ +
+

By default, redirecting to an HTML anchor doesn't work, + because mod_rewrite escapes the # character, + turning it into %23. This, in turn, breaks the + redirection.

+
+ +
Solution:
+ +
+

Use the [NE] flag on the + RewriteRule. NE stands for No Escape. +

+
+ +
Discussion:
+
This technique will of course also work with other + special characters that mod_rewrite, by default, URL-encodes.
+
+ +
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+
+

Time-Dependent Rewriting

+ + + +
+
Description:
+ +
+

We wish to use mod_rewrite to serve different content based on + the time of day.

+
+ +
Solution:
+ +
+

There are a lot of variables named TIME_xxx + for rewrite conditions. In conjunction with the special + lexicographic comparison patterns <STRING, + >STRING and =STRING we can + do time-dependent redirects:

+ +
RewriteEngine on
+RewriteCond   "%{TIME_HOUR}%{TIME_MIN}" ">0700"
+RewriteCond   "%{TIME_HOUR}%{TIME_MIN}" "<1900"
+RewriteRule   "^foo\.html$"             "foo.day.html" [L]
+RewriteRule   "^foo\.html$"             "foo.night.html"
+ + +

This provides the content of foo.day.html + under the URL foo.html from + 07:01-18:59 and at the remaining time the + contents of foo.night.html.

+ +
mod_cache, intermediate proxies + and browsers may each cache responses and cause the either page to be + shown outside of the time-window configured. + mod_expires may be used to control this + effect. You are, of course, much better off simply serving the + content dynamically, and customizing it based on the time of day.
+ +
+
+ +
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+
+

Set Environment Variables Based On URL Parts

+ + + +
+
Description:
+ +
+

At times, we want to maintain some kind of status when we + perform a rewrite. For example, you want to make a note that + you've done that rewrite, so that you can check later to see if a + request came via that rewrite. One way to do this is by setting an + environment variable.

+
+ +
Solution:
+ +
+

Use the [E] flag to set an environment variable.

+ +
RewriteEngine on
+RewriteRule   "^/horse/(.*)"   "/pony/$1" [E=rewritten:1]
+ + +

Later in your ruleset you might check for this environment + variable using a RewriteCond:

+ +
RewriteCond "%{ENV:rewritten}" "=1"
+ + +

Note that environment variables do not survive an external + redirect. You might consider using the [CO] flag to set a + cookie. For per-directory and htaccess rewrites, where the final + substitution is processed as an internal redirect, environment + variables from the previous round of rewriting are prefixed with + "REDIRECT_".

+ +
+
+ +
+
+

Available Languages:  en  | + fr 

+
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Comments

Notice:
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