Build Colm's 'sharding' recipe.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@832309 13f79535-47bb-0310-9956-ffa450edef68

diff --git a/docs/manual/rewrite/rewrite_guide.html.en b/docs/manual/rewrite/rewrite_guide.html.en
index 1d52e5730c50583ff5c5485546eae521f83d26c9..3ab6fb6d0071e10863bb00785a3b9d0b6431f7b8 100644 (file)
--- a/docs/manual/rewrite/rewrite_guide.html.en
+++ b/docs/manual/rewrite/rewrite_guide.html.en
@@ -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 @@ RewriteRule   ^foo\.html$             foo.night.html
 
           <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 @@ while (&lt;&gt;) {
 
     </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 @@ while (&lt;&gt;) {
         <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>