rbowen at apache
Nov 2, 2009, 10:08 PM
Post #1 of 1
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svn commit: r832309 - /httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.html.en
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Author: rbowen
Date: Tue Nov 3 06:08:36 2009
New Revision: 832309
URL: http://svn.apache.org/viewvc?rev=832309&view=rev
Log:
Build Colm's 'sharding' recipe.
Modified:
httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.html.en
Modified: httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.html.en
URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.html.en?rev=832309&r1=832308&r2=832309&view=diff
==============================================================================
--- httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.html.en (original)
+++ httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide.html.en Tue Nov 3 06:08:36 2009
@@ -52,7 +52,7 @@
<li><img alt="" src="../images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#proxy-deny">Proxy Deny</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#external-rewriting">External Rewriting Engine</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#cluster">Web Cluster with Consistent URL Space</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#cluster">URL-based sharding accross multiple backends</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Homedirs</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#browser-dependent-content">Browser Dependent Content</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dynamic-mirror">Dynamic Mirror</a></li>
@@ -401,9 +401,16 @@
<p>This provides the content of <code>foo.day.html</code>
under the URL <code>foo.html</code> from
- <code>07:00-19:00</code> and at the remaining time the
+ <code>07:01-18:59</code> and at the remaining time the
contents of <code>foo.night.html</code>. Just a nice
feature for a homepage...</p>
+
+ <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
+ and browsers may each cache responses and cause the either page to be
+ shown outside of the time-window configured.
+ <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
+ effect.</div>
+
</dd>
</dl>
@@ -500,7 +507,7 @@
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
-<h2><a name="cluster" id="cluster">Web Cluster with Consistent URL Space</a></h2>
+<h2><a name="cluster" id="cluster">URL-based sharding accross multiple backends</a></h2>
@@ -508,67 +515,49 @@
<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.</p>
</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 map files. They look like:</p>
<div class="example"><pre>
-user1 server_of_user1
-user2 server_of_user2
+user1 physical_host_of_user1
+user2 physical_host_of_user2
: :
</pre></div>
- <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 to map;</p>
<div class="example"><pre>
-/u/user/anypath
-/g/group/anypath
-/e/entity/anypath
+/u/user1/anypath
</pre></div>
<p>to</p>
<div class="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></div>
- <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>
<div class="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></div>
</dd>
</dl>
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