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diff --git a/docs/manual/mod/mod_proxy_balancer.html.en b/docs/manual/mod/mod_proxy_balancer.html.en new file mode 100644 index 0000000..ca534bd --- /dev/null +++ b/docs/manual/mod/mod_proxy_balancer.html.en @@ -0,0 +1,363 @@ +<?xml version="1.0" encoding="ISO-8859-1"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head> +<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type" /> +<!-- + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + This file is generated from xml source: DO NOT EDIT + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + --> +<title>mod_proxy_balancer - Apache HTTP Server Version 2.4</title> +<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> +<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> +<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="../style/css/prettify.css" /> +<script src="../style/scripts/prettify.min.js" type="text/javascript"> +</script> + +<link href="../images/favicon.ico" rel="shortcut icon" /></head> +<body> +<div id="page-header"> +<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.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> +<p class="apache">Apache HTTP Server Version 2.4</p> +<img alt="" src="../images/feather.png" /></div> +<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> +<div id="path"> +<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 2.4</a> > <a href="./">Modules</a></div> +<div id="page-content"> +<div id="preamble"><h1>Apache Module mod_proxy_balancer</h1> +<div class="toplang"> +<p><span>Available Languages: </span><a href="../en/mod/mod_proxy_balancer.html" title="English"> en </a> | +<a href="../fr/mod/mod_proxy_balancer.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | +<a href="../ja/mod/mod_proxy_balancer.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p> +</div> +<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> extension for load balancing </td></tr> +<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>proxy_balancer_module</td></tr> +<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_proxy_balancer.c</td></tr> +<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.1 and later</td></tr></table> +<h3>Summary</h3> + + <p>This module <em>requires</em> the service of <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> and it provides load balancing for + all the supported protocols. The most important ones are:</p> + <ul> + <li>HTTP, using <code class="module"><a href="../mod/mod_proxy_http.html">mod_proxy_http</a></code></li> + <li>FTP, using <code class="module"><a href="../mod/mod_proxy_ftp.html">mod_proxy_ftp</a></code></li> + <li>AJP13, using <code class="module"><a href="../mod/mod_proxy_ajp.html">mod_proxy_ajp</a></code></li> + <li>WebSocket, using <code class="module"><a href="../mod/mod_proxy_wstunnel.html">mod_proxy_wstunnel</a></code></li> + </ul> + + <p>The Load balancing scheduler algorithm is not provided by this + module but from other ones such as:</p> + <ul> + <li><code class="module"><a href="../mod/mod_lbmethod_byrequests.html">mod_lbmethod_byrequests</a></code></li> + <li><code class="module"><a href="../mod/mod_lbmethod_bytraffic.html">mod_lbmethod_bytraffic</a></code></li> + <li><code class="module"><a href="../mod/mod_lbmethod_bybusyness.html">mod_lbmethod_bybusyness</a></code></li> + <li><code class="module"><a href="../mod/mod_lbmethod_heartbeat.html">mod_lbmethod_heartbeat</a></code></li> + </ul> + + <p>Thus, in order to get the ability of load balancing, + <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>, <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> + and at least one of load balancing scheduler algorithm modules have + to be present in the server.</p> + + <div class="warning"><h3>Warning</h3> + <p>Do not enable proxying until you have <a href="mod_proxy.html#access">secured your server</a>. Open proxy + servers are dangerous both to your network and to the Internet at + large.</p> + </div> +</div> +<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><h3>Topics</h3> +<ul id="topics"> +<li><img alt="" src="../images/down.gif" /> <a href="#scheduler">Load balancer scheduler algorithm</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#stickyness">Load balancer stickyness</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#example">Examples of a balancer configuration</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#environment">Exported Environment Variables</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#balancer_manager">Enabling Balancer Manager Support</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#stickyness_implementation">Details on load balancer stickyness</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#stickyness_troubleshooting">Troubleshooting load balancer stickyness</a></li> +</ul><h3 class="directives">Directives</h3> +<p>This module provides no + directives.</p> +<h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_proxy_balancer">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_proxy_balancer">Report a bug</a></li></ul><h3>See also</h3> +<ul class="seealso"> +<li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li> +<li><code class="directive"><a href="../mod/mod_proxy.html#balancermember">BalancerMember</a></code></li> +<li><code class="directive"><a href="../mod/mod_proxy.html#balancergrowth">BalancerGrowth</a></code></li> +<li><code class="directive"><a href="../mod/mod_proxy.html#balancerpersist">BalancerPersist</a></code></li> +<li><code class="directive"><a href="../mod/mod_proxy.html#balancerinherit">BalancerInherit</a></code></li> +<li><a href="#comments_section">Comments</a></li></ul></div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="scheduler" id="scheduler">Load balancer scheduler algorithm</a></h2> + + <p>At present, there are 4 load balancer scheduler algorithms available + for use: Request Counting (<code class="module"><a href="../mod/mod_lbmethod_byrequests.html">mod_lbmethod_byrequests</a></code>), + Weighted Traffic Counting (<code class="module"><a href="../mod/mod_lbmethod_bytraffic.html">mod_lbmethod_bytraffic</a></code>), + Pending Request Counting (<code class="module"><a href="../mod/mod_lbmethod_bybusyness.html">mod_lbmethod_bybusyness</a></code>) and + Heartbeat Traffic Counting (<code class="module"><a href="../mod/mod_lbmethod_heartbeat.html">mod_lbmethod_heartbeat</a></code>). + These are controlled via the <code>lbmethod</code> value of + the Balancer definition. See the <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> + directive for more information, especially regarding how to + configure the Balancer and BalancerMembers.</p> +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="stickyness" id="stickyness">Load balancer stickyness</a></h2> + + <p>The balancer supports stickyness. When a request is proxied + to some back-end, then all following requests from the same user + should be proxied to the same back-end. Many load balancers implement + this feature via a table that maps client IP addresses to back-ends. + This approach is transparent to clients and back-ends, but suffers + from some problems: unequal load distribution if clients are themselves + hidden behind proxies, stickyness errors when a client uses a dynamic + IP address that changes during a session and loss of stickyness, if the + mapping table overflows.</p> + <p>The module <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> implements stickyness + on top of two alternative means: cookies and URL encoding. Providing the + cookie can be either done by the back-end or by the Apache web server + itself. The URL encoding is usually done on the back-end.</p> +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="example" id="example">Examples of a balancer configuration</a></h2> + + <p>Before we dive into the technical details, here's an example of + how you might use <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> to provide + load balancing between two back-end servers: + </p> + + <pre class="prettyprint lang-config"><Proxy "balancer://mycluster"> + BalancerMember "http://192.168.1.50:80" + BalancerMember "http://192.168.1.51:80" +</Proxy> +ProxyPass "/test" "balancer://mycluster" +ProxyPassReverse "/test" "balancer://mycluster"</pre> + + + <p>Another example of how to provide load balancing with stickyness + using <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code>, even if the back-end server does + not set a suitable session cookie: + </p> + + <pre class="prettyprint lang-config">Header add Set-Cookie "ROUTEID=.%{BALANCER_WORKER_ROUTE}e; path=/" env=BALANCER_ROUTE_CHANGED +<Proxy "balancer://mycluster"> + BalancerMember "http://192.168.1.50:80" route=1 + BalancerMember "http://192.168.1.51:80" route=2 + ProxySet stickysession=ROUTEID +</Proxy> +ProxyPass "/test" "balancer://mycluster" +ProxyPassReverse "/test" "balancer://mycluster"</pre> + +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="environment" id="environment">Exported Environment Variables</a></h2> + + <p>At present there are 6 environment variables exported:</p> + + <dl> + + <dt><var><a name="balancer_session_sticky" id="balancer_session_sticky">BALANCER_SESSION_STICKY</a></var></dt> + <dd> + <p>This is assigned the <var>stickysession</var> value used for the current + request. It is the name of the cookie or request parameter used for sticky sessions</p> + </dd> + + + <dt><var><a name="balancer_session_route" id="balancer_session_route">BALANCER_SESSION_ROUTE</a></var></dt> + <dd> + <p>This is assigned the <var>route</var> parsed from the current + request.</p> + </dd> + + + <dt><var><a name="balancer_name" id="balancer_name">BALANCER_NAME</a></var></dt> + <dd> + <p>This is assigned the name of the balancer used for the current + request. The value is something like <code>balancer://foo</code>.</p> + </dd> + + + <dt><var><a name="balancer_worker_name" id="balancer_worker_name">BALANCER_WORKER_NAME</a></var></dt> + <dd> + <p>This is assigned the name of the worker used for the current request. + The value is something like <code>http://hostA:1234</code>.</p> + </dd> + + + <dt><var><a name="balancer_worker_route" id="balancer_worker_route">BALANCER_WORKER_ROUTE</a></var></dt> + <dd> + <p>This is assigned the <var>route</var> of the worker that will be + used for the current request.</p> + </dd> + + + <dt><var><a name="balancer_route_changed" id="balancer_route_changed">BALANCER_ROUTE_CHANGED</a></var></dt> + <dd> + <p>This is set to 1 if the session route does not match the + worker route (BALANCER_SESSION_ROUTE != BALANCER_WORKER_ROUTE) or the + session does not yet have an established route. This can be used to + determine when/if the client needs to be sent an updated route + when sticky sessions are used.</p> + </dd> + </dl> + +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="balancer_manager" id="balancer_manager">Enabling Balancer Manager Support</a></h2> + + <p>This module <em>requires</em> the service of + <code class="module"><a href="../mod/mod_status.html">mod_status</a></code>. + Balancer manager enables dynamic update of balancer + members. You can use balancer manager to change the balance + factor of a particular member, or put it in the off line + mode. + </p> + + <p>Thus, in order to get the ability of load balancer management, + <code class="module"><a href="../mod/mod_status.html">mod_status</a></code> and <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> + have to be present in the server.</p> + + <p>To enable load balancer management for browsers from the example.com + domain add this code to your <code>httpd.conf</code> + configuration file</p> +<pre class="prettyprint lang-config"><Location "/balancer-manager"> + SetHandler balancer-manager + Require host example.com +</Location></pre> + + + <p>You can now access load balancer manager by using a Web browser + to access the page + <code>http://your.server.name/balancer-manager</code>. Please note + that only Balancers defined outside of <code><Location ...></code> + containers can be dynamically controlled by the Manager.</p> +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="stickyness_implementation" id="stickyness_implementation">Details on load balancer stickyness</a></h2> + + <p>When using cookie based stickyness, you need to configure the + name of the cookie that contains the information about which back-end + to use. This is done via the <var>stickysession</var> attribute added + to either <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> or + <code class="directive"><a href="../mod/mod_proxy.html#proxyset">ProxySet</a></code>. The name of + the cookie is case-sensitive. The balancer extracts the value of the + cookie and looks for a member worker with <var>route</var> equal + to that value. The <var>route</var> must also be set in either + <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> or + <code class="directive"><a href="../mod/mod_proxy.html#proxyset">ProxySet</a></code>. The cookie can either + be set by the back-end, or as shown in the above + <a href="#example">example</a> by the Apache web server itself.</p> + <p>Some back-ends use a slightly different form of stickyness cookie, + for instance Apache Tomcat. Tomcat adds the name of the Tomcat instance + to the end of its session id cookie, separated with a dot (<code>.</code>) + from the session id. Thus if the Apache web server finds a dot in the value + of the stickyness cookie, it only uses the part behind the dot to search + for the route. In order to let Tomcat know about its instance name, you + need to set the attribute <code>jvmRoute</code> inside the Tomcat + configuration file <code>conf/server.xml</code> to the value of the + <var>route</var> of the worker that connects to the respective Tomcat. + The name of the session cookie used by Tomcat (and more generally by Java + web applications based on servlets) is <code>JSESSIONID</code> + (upper case) but can be configured to something else.</p> + <p>The second way of implementing stickyness is URL encoding. + The web server searches for a query parameter in the URL of the request. + The name of the parameter is specified again using <var>stickysession</var>. + The value of the parameter is used to lookup a member worker with <var>route</var> + equal to that value. Since it is not easy to extract and manipulate all + URL links contained in responses, generally the work of adding the parameters + to each link is done by the back-end generating the content. + In some cases it might be feasible doing + this via the web server using <code class="module"><a href="../mod/mod_substitute.html">mod_substitute</a></code> or + <code class="module"><a href="../mod/mod_sed.html">mod_sed</a></code>. This can have negative impact on performance though.</p> + <p>The Java standards implement URL encoding slightly different. They use + a path info appended to the URL using a semicolon (<code>;</code>) + as the separator and add the session id behind. As in the cookie case, + Apache Tomcat can include the configured <code>jvmRoute</code> in this path + info. To let Apache find this sort of path info, you neet to set + <code>scolonpathdelim</code> to <code>On</code> in + <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> or + <code class="directive"><a href="../mod/mod_proxy.html#proxyset">ProxySet</a></code>.</p> + <p>Finally you can support cookies and URL encoding at the same time, by + configuring the name of the cookie and the name of the URL parameter + separated by a vertical bar (<code>|</code>) as in the following example:</p> + <pre class="prettyprint lang-config">ProxyPass "/test" "balancer://mycluster" stickysession=JSESSIONID|jsessionid scolonpathdelim=On +<Proxy "balancer://mycluster"> + BalancerMember "http://192.168.1.50:80" route=node1 + BalancerMember "http://192.168.1.51:80" route=node2 +</Proxy></pre> + + <p>If the cookie and the request parameter both provide routing information + for the same request, the information from the request parameter is used.</p> +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="stickyness_troubleshooting" id="stickyness_troubleshooting">Troubleshooting load balancer stickyness</a></h2> + + <p>If you experience stickyness errors, e.g. users lose their + application sessions and need to login again, you first want to + check whether this is because the back-ends are sometimes unavailable + or whether your configuration is wrong. To find out about possible + stability problems with the back-ends, check your Apache error log + for proxy error messages.</p> + <p>To verify your configuration, first check, whether the stickyness + is based on a cookie or on URL encoding. Next step would be logging + the appropriate data in the access log by using an enhanced + <code class="directive"><a href="../mod/mod_log_config.html#logformat">LogFormat</a></code>. + The following fields are useful:</p> + <dl> + <dt><code>%{MYCOOKIE}C</code></dt> + <dd>The value contained in the cookie with name <code>MYCOOKIE</code>. + The name should be the same given in the <var>stickysession</var> + attribute.</dd> + <dt><code>%{Set-Cookie}o</code></dt> + <dd>This logs any cookie set by the back-end. You can track, + whether the back-end sets the session cookie you expect, and + to which value it is set.</dd> + <dt><code>%{BALANCER_SESSION_STICKY}e</code></dt> + <dd>The name of the cookie or request parameter used + to lookup the routing information.</dd> + <dt><code>%{BALANCER_SESSION_ROUTE}e</code></dt> + <dd>The route information found in the request.</dd> + <dt><code>%{BALANCER_WORKER_ROUTE}e</code></dt> + <dd>The route of the worker chosen.</dd> + <dt><code>%{BALANCER_ROUTE_CHANGED}e</code></dt> + <dd>Set to <code>1</code> if the route in the request + is different from the route of the worker, i.e. + the request couldn't be handled sticky.</dd> + </dl> + <p>Common reasons for loss of session are session timeouts, + which are usually configurable on the back-end server.</p> + <p>The balancer also logs detailed information about handling + stickyness to the error log, if the log level is set to + <code>debug</code> or higher. This is an easy way to + troubleshoot stickyness problems, but the log volume might + be to high for production servers under high load.</p> +</div> +</div> +<div class="bottomlang"> +<p><span>Available Languages: </span><a href="../en/mod/mod_proxy_balancer.html" title="English"> en </a> | +<a href="../fr/mod/mod_proxy_balancer.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | +<a href="../ja/mod/mod_proxy_balancer.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p> +</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. 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