colm at apache
Nov 2, 2009, 6:02 PM
Post #1 of 1
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svn commit: r832261 - /httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.xml
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Author: colm
Date: Tue Nov 3 02:02:23 2009
New Revision: 832261
URL: http://svn.apache.org/viewvc?rev=832261&view=rev
Log:
Rewrite the "cluster" section of the rewrite docs. Changes;
* Call the technique "sharding" - like the rest of the world does.
* Simplify to just one example use-case, sharding users.
* Make the usage of the term "physical host" consistent.
* Remove unreachable nonsense rewrite rules
* Remove redundant sentences.
Modified:
httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.xml
Modified: httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.xml
URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.xml?rev=832261&r1=832260&r2=832261&view=diff
==============================================================================
--- httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.xml (original)
+++ httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.xml Tue Nov 3 02:02:23 2009
@@ -488,73 +488,55 @@
<section id="cluster">
- <title>Web Cluster with Consistent URL Space</title>
+ <title>URL-based sharding accross multiple backends</title>
<dl>
<dt>Description:</dt>
<dd>
- <p>We want to create a homogeneous and consistent URL
- layout across all WWW servers on an Intranet web cluster, i.e.,
- all URLs (by definition server-local and thus
- server-dependent!) become server <em>independent</em>!
- What we want is to give the WWW namespace a single consistent
- layout: no URL should refer to
- any particular target server. The cluster itself
- should connect users automatically to a physical target
- host as needed, invisibly.</p>
+ <p>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 seperate
+ backend servers.
</dd>
<dt>Solution:</dt>
<dd>
- <p>First, the knowledge of the target servers comes from
- (distributed) external maps which contain information on
- where our users, groups, and entities reside. They have the
- form:</p>
+ <p>A mapping is maintained, from users to target servers, in
+ external maps files. They look like:</p>
<example><pre>
-user1 server_of_user1
-user2 server_of_user2
+user1 physical_host_of_user1
+user2 physical_host_of_user2
: :
</pre></example>
- <p>We put them into files <code>map.xxx-to-host</code>.
- Second we need to instruct all servers to redirect URLs
- of the forms:</p>
+ <p>We put this into a <code>map.users-to-hosts</code> file. The
+ aim is the map;</p>
<example><pre>
-/u/user/anypath
-/g/group/anypath
-/e/entity/anypath
+/u/user1/anypath
</pre></example>
<p>to</p>
<example><pre>
-http://physical-host/u/user/anypath
-http://physical-host/g/group/anypath
-http://physical-host/e/entity/anypath
+http://physical_host_of_user1/u/user/anypath
</pre></example>
- <p>when any URL path need not be valid on every server. 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):</p>
+ <p>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):</p>
<example><pre>
RewriteEngine on
-RewriteMap user-to-host txt:/path/to/map.user-to-host
-RewriteMap group-to-host txt:/path/to/map.group-to-host
-RewriteMap entity-to-host txt:/path/to/map.entity-to-host
-
-RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${user-to-host:$1|server0}</strong>/u/$1/$2
-RewriteRule ^/g/<strong>([^/]+)</strong>/?(.*) http://<strong>${group-to-host:$1|server0}</strong>/g/$1/$2
-RewriteRule ^/e/<strong>([^/]+)</strong>/?(.*) http://<strong>${entity-to-host:$1|server0}</strong>/e/$1/$2
+RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts
-RewriteRule ^/([uge])/([^/]+)/?$ /$1/$2/.www/
-RewriteRule ^/([uge])/([^/]+)/([^.]+.+) /$1/$2/.www/$3\
+RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${users-to-hosts:$1|server0}</strong>/u/$1/$2
</pre></example>
</dd>
</dl>
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