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Extensible Markup Language  |  2007-12-15  |  17KB  |  370 lines
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  8. <title>mod_proxy_balancer - Apache HTTP Server</title>
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  14. <div id="page-header">
  15. <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
  16. <p class="apache">Apache HTTP Server Version 2.2</p>
  17. <img alt="" src="../images/feather.gif" /></div>
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  20. <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 2.2</a> > <a href="./">Modules</a></div>
  21. <div id="page-content">
  22. <div id="preamble"><h1>Apache Module mod_proxy_balancer</h1>
  23. <div class="toplang">
  24. <p><span>Available Languages: </span><a href="../en/mod/mod_proxy_balancer.html" title="English"> en </a> |
  25. <a href="../ja/mod/mod_proxy_balancer.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
  26. </div>
  27. <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>
  28. <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
  29. <tr><th><a href="module-dict.html#ModuleIdentifier">ModuleáIdentifier:</a></th><td>proxy_balancer_module</td></tr>
  30. <tr><th><a href="module-dict.html#SourceFile">SourceáFile:</a></th><td>proxy_balancer.c</td></tr>
  31. <tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.1 and later</td></tr></table>
  32. <h3>Summary</h3>
  33.  
  34.     <p>This module <em>requires</em> the service of <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>. It provides load balancing support for
  35.     <code>HTTP</code>, <code>FTP</code> and <code>AJP13</code> protocols
  36.     </p>
  37.  
  38.     <p>Thus, in order to get the ability of load balancing,
  39.     <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> and <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code>
  40.     have to be present in the server.</p>
  41.  
  42.     <div class="warning"><h3>Warning</h3>
  43.       <p>Do not enable proxying until you have <a href="mod_proxy.html#access">secured your server</a>. Open proxy
  44.       servers are dangerous both to your network and to the Internet at
  45.       large.</p>
  46.     </div>
  47. </div>
  48. <div id="quickview"><h3 class="directives">Directives</h3>
  49. <p>This module provides no
  50.             directives.</p>
  51. <h3>Topics</h3>
  52. <ul id="topics">
  53. <li><img alt="" src="../images/down.gif" /> <a href="#scheduler">Load balancer scheduler algorithm</a></li>
  54. <li><img alt="" src="../images/down.gif" /> <a href="#requests">Request Counting Algorithm</a></li>
  55. <li><img alt="" src="../images/down.gif" /> <a href="#traffic">Weighted Traffic Counting Algorithm</a></li>
  56. <li><img alt="" src="../images/down.gif" /> <a href="#environment">Exported Environment Variables</a></li>
  57. <li><img alt="" src="../images/down.gif" /> <a href="#enable">Enabling Balancer Manager Support</a></li>
  58. </ul><h3>See also</h3>
  59. <ul class="seealso">
  60. <li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li>
  61. </ul></div>
  62. <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  63. <div class="section">
  64. <h2><a name="scheduler" id="scheduler">Load balancer scheduler algorithm</a></h2>
  65.     
  66.     <p>At present, there are 2 load balancer scheduler algorithms available
  67.     for use: Request Counting and Weighted Traffic Counting. These are controlled
  68.     via the <code>lbmethod</code> value of the Balancer definition. See
  69.     the <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> directive for
  70.     more information.</p>
  71.  
  72. </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  73. <div class="section">
  74. <h2><a name="requests" id="requests">Request Counting Algorithm</a></h2>
  75.     
  76.     <p>Enabled via <code>lbmethod=byrequests</code>, the idea behind this
  77.     scheduler is that we distribute the requests among the
  78.     various workers to ensure that each gets their configured share
  79.     of the number of requests. It works as follows:</p>
  80.  
  81.     <p><dfn>lbfactor</dfn> is <em>how much we expect this worker
  82.     to work</em>, or <em>the workers's work quota</em>. This is
  83.     a normalized value representing their "share" of the amount of
  84.     work to be done.</p>
  85.  
  86.     <p><dfn>lbstatus</dfn> is <em>how urgent this worker has to work
  87.     to fulfill its quota of work</em>.</p>
  88.  
  89.     <p>The <dfn>worker</dfn> is a member of the load balancer,
  90.     usually a remote host serving one of the supported protocols.</p>
  91.  
  92.     <p>We distribute each worker's work quota to the worker, and then look
  93.     which of them needs to work most urgently (biggest lbstatus).  This
  94.     worker is then selected for work, and its lbstatus reduced by the
  95.     total work quota we distributed to all workers.  Thus the sum of all
  96.     lbstatus does not change(*) and we distribute the requests
  97.     as desired.</p>
  98.  
  99.     <p>If some workers are disabled, the others will
  100.     still be scheduled correctly.</p>
  101.  
  102.     <div class="example"><pre><code>for each worker in workers
  103.     worker lbstatus += worker lbfactor
  104.     total factor    += worker lbfactor
  105.     if worker lbstatus > candidate lbstatus
  106.         candidate = worker
  107.  
  108. candidate lbstatus -= total factor</code></pre></div>
  109.  
  110.     <p>If a balancer is configured as follows:</p>
  111.     
  112.     <table><tr><th>worker</th>
  113.         <th class="data">a</th>
  114.         <th class="data">b</th>
  115.         <th class="data">c</th>
  116.         <th class="data">d</th></tr>
  117. <tr><th>lbfactor</th>
  118.         <td class="data">25</td>
  119.         <td class="data">25</td>
  120.         <td class="data">25</td>
  121.         <td class="data">25</td></tr>
  122. <tr><th>lbstatus</th>
  123.         <td class="data">0</td>
  124.         <td class="data">0</td>
  125.         <td class="data">0</td>
  126.         <td class="data">0</td></tr>
  127. </table>
  128.  
  129.     <p>And <var>b</var> gets disabled, the following schedule is produced:</p>
  130.  
  131.     <table><tr><th>worker</th>
  132.         <th class="data">a</th>
  133.         <th class="data">b</th>
  134.         <th class="data">c</th>
  135.         <th class="data">d</th></tr>
  136. <tr><th>lbstatus</th>
  137.         <td class="data"><em>-50</em></td>
  138.         <td class="data">0</td>
  139.         <td class="data">25</td>
  140.         <td class="data">25</td></tr>
  141. <tr><th>lbstatus</th>
  142.         <td class="data">-25</td>
  143.         <td class="data">0</td>
  144.         <td class="data"><em>-25</em></td>
  145.         <td class="data">50</td></tr>
  146. <tr><th>lbstatus</th>
  147.         <td class="data">0</td>
  148.         <td class="data">0</td>
  149.         <td class="data">0</td>
  150.         <td class="data"><em>0</em></td></tr>
  151. <tr><td class="data" colspan="5">(repeat)</td></tr>
  152. </table>
  153.  
  154.     <p>That is it schedules: <var>a</var> <var>c</var> <var>d</var>
  155.     <var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var>
  156.     <var>d</var> ... Please note that:</p>
  157.  
  158.     <table><tr><th>worker</th>
  159.         <th class="data">a</th>
  160.         <th class="data">b</th>
  161.         <th class="data">c</th>
  162.         <th class="data">d</th></tr>
  163. <tr><th>lbfactor</th>
  164.         <td class="data">25</td>
  165.         <td class="data">25</td>
  166.         <td class="data">25</td>
  167.         <td class="data">25</td></tr>
  168. </table>
  169.  
  170.     <p>Has the exact same behavior as:</p>
  171.  
  172.     <table><tr><th>worker</th>
  173.         <th class="data">a</th>
  174.         <th class="data">b</th>
  175.         <th class="data">c</th>
  176.         <th class="data">d</th></tr>
  177. <tr><th>lbfactor</th>
  178.         <td class="data">1</td>
  179.         <td class="data">1</td>
  180.         <td class="data">1</td>
  181.         <td class="data">1</td></tr>
  182. </table>
  183.  
  184.     <p>This is because all values of <dfn>lbfactor</dfn> are normalized
  185.     with respect to the others. For:</p>
  186.  
  187.     <table><tr><th>worker</th>
  188.         <th class="data">a</th>
  189.         <th class="data">b</th>
  190.         <th class="data">c</th></tr>
  191. <tr><th>lbfactor</th>
  192.         <td class="data">1</td>
  193.         <td class="data">4</td>
  194.         <td class="data">1</td></tr>
  195. </table>
  196.  
  197.     <p>worker <var>b</var> will, on average, get 4 times the requests
  198.     that <var>a</var> and <var>c</var> will.</p>
  199.  
  200.     <p>The following asymmetric configuration works as one would expect:</p>
  201.  
  202.     <table><tr><th>worker</th>
  203.         <th class="data">a</th>
  204.         <th class="data">b</th></tr>
  205. <tr><th>lbfactor</th>
  206.         <td class="data">70</td>
  207.         <td class="data">30</td></tr>
  208. <tr><td class="data" colspan="2"> </td></tr>
  209. <tr><th>lbstatus</th>
  210.         <td class="data"><em>-30</em></td>
  211.         <td class="data">30</td></tr>
  212. <tr><th>lbstatus</th>
  213.         <td class="data">40</td>
  214.         <td class="data"><em>-40</em></td></tr>
  215. <tr><th>lbstatus</th>
  216.         <td class="data"><em>10</em></td>
  217.         <td class="data">-10</td></tr>
  218. <tr><th>lbstatus</th>
  219.         <td class="data"><em>-20</em></td>
  220.         <td class="data">20</td></tr>
  221. <tr><th>lbstatus</th>
  222.         <td class="data"><em>-50</em></td>
  223.         <td class="data">50</td></tr>
  224. <tr><th>lbstatus</th>
  225.         <td class="data">20</td>
  226.         <td class="data"><em>-20</em></td></tr>
  227. <tr><th>lbstatus</th>
  228.         <td class="data"><em>-10</em></td>
  229.         <td class="data">10</td></tr>
  230. <tr><th>lbstatus</th>
  231.         <td class="data"><em>-40</em></td>
  232.         <td class="data">40</td></tr>
  233. <tr><th>lbstatus</th>
  234.         <td class="data">30</td>
  235.         <td class="data"><em>-30</em></td></tr>
  236. <tr><th>lbstatus</th>
  237.         <td class="data"><em>0</em></td>
  238.         <td class="data">0</td></tr>
  239. <tr><td class="data" colspan="3">(repeat)</td></tr>
  240. </table>
  241.  
  242.     <p>That is after 10 schedules, the schedule repeats and 7 <var>a</var>
  243.     are selected with 3 <var>b</var> interspersed.</p>
  244. </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  245. <div class="section">
  246. <h2><a name="traffic" id="traffic">Weighted Traffic Counting Algorithm</a></h2>
  247.     
  248.     <p>Enabled via <code>lbmethod=bytraffic</code>, the idea behind this
  249.     scheduler is very similar to the Request Counting method, with
  250.     the following changes:</p>
  251.  
  252.     <p><dfn>lbfactor</dfn> is <em>how much traffic, in bytes, we want
  253.     this worker to handle</em>. This is also a normalized value
  254.     representing their "share" of the amount of work to be done,
  255.     but instead of simply counting the number of requests, we take
  256.     into account the amount of traffic this worker has seen.</p>
  257.  
  258.     <p>If a balancer is configured as follows:</p>
  259.     
  260.     <table><tr><th>worker</th>
  261.         <th class="data">a</th>
  262.         <th class="data">b</th>
  263.         <th class="data">c</th></tr>
  264. <tr><th>lbfactor</th>
  265.         <td class="data">1</td>
  266.         <td class="data">2</td>
  267.         <td class="data">1</td></tr>
  268. </table>
  269.  
  270.     <p>Then we mean that we want <var>b</var> to process twice the
  271.     amount of bytes than <var>a</var> or <var>c</var> should. It does
  272.     not necessarily mean that <var>b</var> would handle twice as
  273.     many requests, but it would process twice the I/O. Thus, the
  274.     size of the request and response are applied to the weighting
  275.     and selection algorithm.</p>
  276.  
  277. </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  278. <div class="section">
  279. <h2><a name="environment" id="environment">Exported Environment Variables</a></h2>
  280.     
  281.     <p>At present there are 6 environment variables exported:</p>
  282.  
  283.     <dl>
  284.     
  285.     <dt><var><a name="balancer_session_sticky" id="balancer_session_sticky">BALANCER_SESSION_STICKY</a></var></dt>
  286.     <dd>
  287.     <p>This is assigned the <var>stickysession</var> value used in the current
  288.     request.  It is the cookie or parameter name used for sticky sessions</p>
  289.     </dd>
  290.  
  291.     
  292.     <dt><var><a name="balancer_session_route" id="balancer_session_route">BALANCER_SESSION_ROUTE</a></var></dt>
  293.     <dd>
  294.     <p>This is assigned the <var>route</var> parsed from the current 
  295.     request.</p>
  296.     </dd>
  297.  
  298.     
  299.     <dt><var><a name="balancer_name" id="balancer_name">BALANCER_NAME</a></var></dt>
  300.     <dd>
  301.     <p>This is assigned the name of the balancer used for the current 
  302.     request. The value is something like <code>balancer://foo</code>.</p>
  303.     </dd>
  304.  
  305.     
  306.     <dt><var><a name="balancer_worker_name" id="balancer_worker_name">BALANCER_WORKER_NAME</a></var></dt>
  307.     <dd>
  308.     <p>This is assigned the name of the worker used for the current request.
  309.     The value is something like <code>http://hostA:1234</code>.</p>
  310.     </dd>
  311.  
  312.     
  313.     <dt><var><a name="balancer_worker_route" id="balancer_worker_route">BALANCER_WORKER_ROUTE</a></var></dt>
  314.     <dd>
  315.     <p>This is assigned the <var>route</var> of the worker that will be 
  316.     used for the current request.</p>
  317.     </dd>
  318.  
  319.     
  320.     <dt><var><a name="balancer_route_changed" id="balancer_route_changed">BALANCER_ROUTE_CHANGED</a></var></dt>
  321.     <dd>
  322.     <p>This is set to 1 if the session route does not match the
  323.     worker route (BALANCER_SESSION_ROUTE != BALANCER_WORKER_ROUTE) or the
  324.     session does not yet have an established route.  This can be used to
  325.     determine when/if the client needs to be sent an updated route
  326.     when sticky sessions are used.</p>
  327.     </dd>
  328.     </dl>
  329.  
  330. </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  331. <div class="section">
  332. <h2><a name="enable" id="enable">Enabling Balancer Manager Support</a></h2>
  333.     
  334.     <p>This module <em>requires</em> the service of 
  335.     <code class="module"><a href="../mod/mod_status.html">mod_status</a></code>.
  336.     Balancer manager enables dynamic update of balancer
  337.     members. You can use balancer manager to change the balance
  338.     factor or a particular member, or put it in the off line
  339.     mode.
  340.     </p>
  341.  
  342.     <p>Thus, in order to get the ability of load balancer management,
  343.     <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>
  344.     have to be present in the server.</p>
  345.  
  346.     <p>To enable load balancer management for browsers from the foo.com
  347.     domain add this code to your <code>httpd.conf</code>
  348.     configuration file</p>
  349. <div class="example"><p><code>
  350.     <Location /balancer-manager><br />
  351.     SetHandler balancer-manager<br />
  352. <br />
  353.     Order Deny,Allow<br />
  354.     Deny from all<br />
  355.     Allow from .foo.com<br />
  356.     </Location>
  357. </code></p></div>
  358.  
  359.     <p>You can now access load balancer manager by using a Web browser
  360.     to access the page
  361.     <code>http://your.server.name/balancer-manager</code></p>
  362. </div>
  363. </div>
  364. <div class="bottomlang">
  365. <p><span>Available Languages: </span><a href="../en/mod/mod_proxy_balancer.html" title="English"> en </a> |
  366. <a href="../ja/mod/mod_proxy_balancer.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
  367. </div><div id="footer">
  368. <p class="apache">Copyright 2007 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
  369. <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
  370. </body></html>