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63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p>
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63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Modules</a></div>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<p><span>Available Languages: </span><a href="/en/mod/mod_proxy_ajp.html" title="English"> en </a> |
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63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>AJP support module for
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code></td></tr>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>proxy_ajp_module</td></tr>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>mod_proxy_ajp.c</td></tr></table>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>This module <em>requires</em> the service of <code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code>. It provides support for the
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <code>Apache JServ Protocol version 1.3</code> (hereafter
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>Thus, in order to get the ability of handling <code>AJP13</code>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end protocol, <code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code> and
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <code class="module"><a href="/mod/mod_proxy_ajp.html">mod_proxy_ajp</a></code> have to be present in the server.</p>
ecc5150d35c0dc5ee5119c2717e6660fa331abbftakashi <p>Do not enable proxying until you have <a href="mod_proxy.html#access">secured your server</a>. Open proxy
4a7be288e6fc28a6cb940e26542dbf574bc907b9pctony servers are dangerous both to your network and to the Internet at
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<div id="quickview"><h3 class="directives">Directives</h3>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<p>This module provides no
e1e8390280254f7f0580d701e583f670643d4f3fnilgun directives.</p>
e1e8390280254f7f0580d701e583f670643d4f3fnilgun<li><img alt="" src="/images/down.gif" /> <a href="#usage">Usage</a></li>
e1e8390280254f7f0580d701e583f670643d4f3fnilgun<li><img alt="" src="/images/down.gif" /> <a href="#env">Environment Variables</a></li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<li><img alt="" src="/images/down.gif" /> <a href="#overviewprotocol">Overview of the protocol</a></li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<li><img alt="" src="/images/down.gif" /> <a href="#basppacketstruct">Basic Packet Structure</a></li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<li><img alt="" src="/images/down.gif" /> <a href="#rpacetstruct">Request Packet Structure</a></li>
08cf4a15275e4cb65a424b3a1db5410bfb51085cjim<li><img alt="" src="/images/down.gif" /> <a href="#resppacketstruct">Response Packet Structure</a></li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<li><code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code></li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<li><a href="/env.html">Environment Variable documentation</a></li>
1ac39787115a288f5e848344b1b1e8dccb1c58f1nd</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
1ac39787115a288f5e848344b1b1e8dccb1c58f1nd<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>This module is used to reverse proxy to a backend application server
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end (e.g. Apache Tomcat) using the AJP13 protocol. The usage is similar to
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end an HTTP reverse proxy, but uses the <code>ajp://</code> prefix:</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <div class="example"><h3>Simple Reverse Proxy</h3><pre class="prettyprint lang-config">
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <div class="example"><h3>Balancer Reverse Proxy</h3><pre class="prettyprint lang-config">
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<Proxy balancer://cluster>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end BalancerMember ajp://app1.example.com:8009 loadfactor=1
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end BalancerMember ajp://app2.example.com:8009 loadfactor=2
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end ProxySet lbmethod=bytraffic
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end</Proxy>
f3ec420152ca921e4c1ce77782f51b53f659018dnd <p>Note that usually no
f3ec420152ca921e4c1ce77782f51b53f659018dnd <code class="directive"><a href="/mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a></code>
08cf4a15275e4cb65a424b3a1db5410bfb51085cjim directive is necessary. The AJP request includes the original host
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end header given to the proxy, and the application server can be expected
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end to generate self-referential headers relative to this host, so no
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end rewriting is necessary.</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>The main exception is when the URL path on the proxy differs from that
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end backend. In this case, a redirect header can be rewritten relative to the
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end original host URL (not the backend <code>ajp://</code> URL), for
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end example:</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <div class="example"><h3>Rewriting Proxied Path</h3><pre class="prettyprint lang-config">
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>However, it is usually better to deploy the application on the backend
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end server at the same path as the proxy rather than to take this approach.
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>Environment variables whose names have the prefix <code>AJP_</code>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end are forwarded to the origin server as AJP request attributes
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end (with the AJP_ prefix removed from the name of the key).</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end<h2><a name="overviewprotocol" id="overviewprotocol">Overview of the protocol</a></h2>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>The <code>AJP13</code> protocol is packet-oriented. A binary format
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end was presumably chosen over the more readable plain text for reasons of
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end performance. The web server communicates with the servlet container over
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end TCP connections. To cut down on the expensive process of socket creation,
d0828c8a321dc5e9ea60550f052294669c08cf93jim the web server will attempt to maintain persistent TCP connections to the
d0828c8a321dc5e9ea60550f052294669c08cf93jim servlet container, and to reuse a connection for multiple request/response
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end cycles.</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>Once a connection is assigned to a particular request, it will not be
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end used for any others until the request-handling cycle has terminated. In
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end other words, requests are not multiplexed over connections. This makes
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end for much simpler code at either end of the connection, although it does
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end cause more connections to be open at once.</p>
2704de98885368683621b01c8f8f4e4b01557611takashi <p>Once the web server has opened a connection to the servlet container,
2704de98885368683621b01c8f8f4e4b01557611takashi the connection can be in one of the following states:</p>
d0828c8a321dc5e9ea60550f052294669c08cf93jim <li> Idle <br /> No request is being handled over this connection. </li>
2704de98885368683621b01c8f8f4e4b01557611takashi <li> Assigned <br /> The connection is handling a specific request.</li>
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi <p>Once a connection is assigned to handle a particular request, the basic
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi request information (e.g. HTTP headers, etc) is sent over the connection in
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi a highly condensed form (e.g. common strings are encoded as integers).
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi Details of that format are below in Request Packet Structure. If there is a
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi body to the request <code>(content-length > 0)</code>, that is sent in a
cd6c8de3bedcc401ee230159b0439fa20f44488etakashi separate packet immediately after.</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>At this point, the servlet container is presumably ready to start
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end processing the request. As it does so, it can send the
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end following messages back to the web server:</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <li>SEND_HEADERS <br />Send a set of headers back to the browser.</li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <li>SEND_BODY_CHUNK <br />Send a chunk of body data back to the browser.
d87bca6b7382e9f3648aec4fb3419b225c39ee41jim <li>GET_BODY_CHUNK <br />Get further data from the request if it hasn't all
d87bca6b7382e9f3648aec4fb3419b225c39ee41jim been transferred yet. This is necessary because the packets have a fixed
27d778df0b517e1578f907d2e51eb961cd8ee5fbjim maximum size and arbitrary amounts of data can be included the body of a
27d778df0b517e1578f907d2e51eb961cd8ee5fbjim request (for uploaded files, for example). (Note: this is unrelated to
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end HTTP chunked transfer).</li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <li>END_RESPONSE <br /> Finish the request-handling cycle.</li>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>Each message is accompanied by a differently formatted packet of data.
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end See Response Packet Structures below for details.</p>
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
604c89126c27104f659d7a51b0113e3bd435faf8fielding<h2><a name="basppacketstruct" id="basppacketstruct">Basic Packet Structure</a></h2>
50cb7e2b30597f481fee57bac945190f06ebcc58jorton <p>There is a bit of an XDR heritage to this protocol, but it differs
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end in lots of ways (no 4 byte alignment, for example).</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>Byte order: I am not clear about the endian-ness of the individual
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end bytes. I'm guessing the bytes are little-endian, because that's what
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end XDR specifies, and I'm guessing that sys/socket library is magically
0a69d9bb491d9810892a9949c01403a1de3c7ac2nd making that so (on the C side). If anyone with a better knowledge of
5f4e50966b2b9b58436a1651cbe588d1b595657ewrowe socket calls can step in, that would be great.</p>
5f4e50966b2b9b58436a1651cbe588d1b595657ewrowe <p>There are four data types in the protocol: bytes, booleans,
5f4e50966b2b9b58436a1651cbe588d1b595657ewrowe integers and strings.</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <dd>A single byte, <code>1 = true</code>, <code>0 = false</code>.
50cb7e2b30597f481fee57bac945190f06ebcc58jorton Using other non-zero values as true (i.e. C-style) may work in some places,
79b024b81f6bb3c44dce77a7552191daf8b522d2jim but it won't in others.</dd>
f772e8f448c223e5ea306f1bf92d97d968f972d5jim <dd>A number in the range of <code>0 to 2^16 (32768)</code>. Stored in
4a7be288e6fc28a6cb940e26542dbf574bc907b9pctony 2 bytes with the high-order byte first.</dd>
d87bca6b7382e9f3648aec4fb3419b225c39ee41jim <dd>A variable-sized string (length bounded by 2^16). Encoded with
d87bca6b7382e9f3648aec4fb3419b225c39ee41jim the length packed into two bytes first, followed by the string
f3ec420152ca921e4c1ce77782f51b53f659018dnd (including the terminating '\0'). Note that the encoded length does
f3ec420152ca921e4c1ce77782f51b53f659018dnd <strong>not</strong> include the trailing '\0' -- it is like
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <code>strlen</code>. This is a touch confusing on the Java side, which
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end is littered with odd autoincrement statements to skip over these
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end terminators. I believe the reason this was done was to allow the C
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end code to be extra efficient when reading strings which the servlet
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end container is sending back -- with the terminating \0 character, the
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi C code can pass around references into a single buffer, without copying.
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end if the \0 was missing, the C code would have to copy things out in order
e1e8390280254f7f0580d701e583f670643d4f3fnilgun to get its notion of a string.</dd>
987153b0772b889900365647b5afb962b80b4439nilgun <p>According to much of the code, the max packet size is <code>
e1e8390280254f7f0580d701e583f670643d4f3fnilgun 8 * 1024 bytes (8K)</code>. The actual length of the packet is encoded in
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end the header.</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <p>Packets sent from the server to the container begin with
1d980e5489836e977ba59b419e27b0ec875c4bd3takashi <code>0x1234</code>. Packets sent from the container to the server
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end begin with <code>AB</code> (that's the ASCII code for A followed by the
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end ASCII code for B). After those first two bytes, there is an integer
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end (encoded as above) with the length of the payload. Although this might
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end suggest that the maximum payload could be as large as 2^16, in fact, the
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end code sets the maximum to be 8K.</p>
63f06dce77bb2d9b1c5aa5deeb47a1069987fd1end <th colspan="6"><em>Packet Format (Server->Container)</em></th>
If there is no more data in the body (i.e. the servlet container is
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