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| <p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_proxy_balancer.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_proxy_balancer</h1> |
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| <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>. It provides load balancing support for |
| <code>HTTP</code>, <code>FTP</code> and <code>AJP13</code> protocols |
| </p> |
| |
| <p>Thus, in order to get the ability of load balancing, |
| <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> |
| 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"><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="#requests">Request Counting Algorithm</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#traffic">Weighted Traffic Counting Algorithm</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#busyness">Pending Request Counting Algorithm</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>See also</h3> |
| <ul class="seealso"> |
| <li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li> |
| </ul><ul class="seealso"><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 3 load balancer scheduler algorithms available |
| for use: Request Counting, Weighted Traffic Counting and Pending Request |
| Counting. 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.</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> |
| |
| <div class="example"><p><code> |
| <Proxy balancer://mycluster><br /> |
| BalancerMember http://192.168.1.50:80<br /> |
| BalancerMember http://192.168.1.51:80<br /> |
| </Proxy><br /> |
| ProxyPass /test balancer://mycluster |
| </code></p></div> |
| |
| <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> |
| |
| <div class="example"><p><code> |
| Header add Set-Cookie "ROUTEID=.%{BALANCER_WORKER_ROUTE}e; path=/" |
| env=BALANCER_ROUTE_CHANGED<br /> |
| <Proxy balancer://mycluster><br /> |
| BalancerMember http://192.168.1.50:80 route=1<br /> |
| BalancerMember http://192.168.1.51:80 route=2<br /> |
| ProxySet stickysession=ROUTEID<br /> |
| </Proxy><br /> |
| ProxyPass /test balancer://mycluster |
| </code></p></div> |
| </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="requests" id="requests">Request Counting Algorithm</a></h2> |
| |
| <p>Enabled via <code>lbmethod=byrequests</code>, the idea behind this |
| scheduler is that we distribute the requests among the |
| various workers to ensure that each gets their configured share |
| of the number of requests. It works as follows:</p> |
| |
| <p><dfn>lbfactor</dfn> is <em>how much we expect this worker |
| to work</em>, or <em>the workers's work quota</em>. This is |
| a normalized value representing their "share" of the amount of |
| work to be done.</p> |
| |
| <p><dfn>lbstatus</dfn> is <em>how urgent this worker has to work |
| to fulfill its quota of work</em>.</p> |
| |
| <p>The <dfn>worker</dfn> is a member of the load balancer, |
| usually a remote host serving one of the supported protocols.</p> |
| |
| <p>We distribute each worker's work quota to the worker, and then look |
| which of them needs to work most urgently (biggest lbstatus). This |
| worker is then selected for work, and its lbstatus reduced by the |
| total work quota we distributed to all workers. Thus the sum of all |
| lbstatus does not change(*) and we distribute the requests |
| as desired.</p> |
| |
| <p>If some workers are disabled, the others will |
| still be scheduled correctly.</p> |
| |
| <div class="example"><pre><code>for each worker in workers |
| worker lbstatus += worker lbfactor |
| total factor += worker lbfactor |
| if worker lbstatus > candidate lbstatus |
| candidate = worker |
| |
| candidate lbstatus -= total factor</code></pre></div> |
| |
| <p>If a balancer is configured as follows:</p> |
| |
| <table><tr><th>worker</th> |
| <th class="data">a</th> |
| <th class="data">b</th> |
| <th class="data">c</th> |
| <th class="data">d</th></tr> |
| <tr><th>lbfactor</th> |
| <td class="data">25</td> |
| <td class="data">25</td> |
| <td class="data">25</td> |
| <td class="data">25</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data">0</td> |
| <td class="data">0</td> |
| <td class="data">0</td> |
| <td class="data">0</td></tr> |
| </table> |
| |
| <p>And <var>b</var> gets disabled, the following schedule is produced:</p> |
| |
| <table><tr><th>worker</th> |
| <th class="data">a</th> |
| <th class="data">b</th> |
| <th class="data">c</th> |
| <th class="data">d</th></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>-50</em></td> |
| <td class="data">0</td> |
| <td class="data">25</td> |
| <td class="data">25</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data">-25</td> |
| <td class="data">0</td> |
| <td class="data"><em>-25</em></td> |
| <td class="data">50</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data">0</td> |
| <td class="data">0</td> |
| <td class="data">0</td> |
| <td class="data"><em>0</em></td></tr> |
| <tr><td class="data" colspan="5">(repeat)</td></tr> |
| </table> |
| |
| <p>That is it schedules: <var>a</var> <var>c</var> <var>d</var> |
| <var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var> |
| <var>d</var> ... Please note that:</p> |
| |
| <table><tr><th>worker</th> |
| <th class="data">a</th> |
| <th class="data">b</th> |
| <th class="data">c</th> |
| <th class="data">d</th></tr> |
| <tr><th>lbfactor</th> |
| <td class="data">25</td> |
| <td class="data">25</td> |
| <td class="data">25</td> |
| <td class="data">25</td></tr> |
| </table> |
| |
| <p>Has the exact same behavior as:</p> |
| |
| <table><tr><th>worker</th> |
| <th class="data">a</th> |
| <th class="data">b</th> |
| <th class="data">c</th> |
| <th class="data">d</th></tr> |
| <tr><th>lbfactor</th> |
| <td class="data">1</td> |
| <td class="data">1</td> |
| <td class="data">1</td> |
| <td class="data">1</td></tr> |
| </table> |
| |
| <p>This is because all values of <dfn>lbfactor</dfn> are normalized |
| with respect to the others. For:</p> |
| |
| <table><tr><th>worker</th> |
| <th class="data">a</th> |
| <th class="data">b</th> |
| <th class="data">c</th></tr> |
| <tr><th>lbfactor</th> |
| <td class="data">1</td> |
| <td class="data">4</td> |
| <td class="data">1</td></tr> |
| </table> |
| |
| <p>worker <var>b</var> will, on average, get 4 times the requests |
| that <var>a</var> and <var>c</var> will.</p> |
| |
| <p>The following asymmetric configuration works as one would expect:</p> |
| |
| <table><tr><th>worker</th> |
| <th class="data">a</th> |
| <th class="data">b</th></tr> |
| <tr><th>lbfactor</th> |
| <td class="data">70</td> |
| <td class="data">30</td></tr> |
| <tr><td class="data" colspan="2"> </td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>-30</em></td> |
| <td class="data">30</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data">40</td> |
| <td class="data"><em>-40</em></td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>10</em></td> |
| <td class="data">-10</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>-20</em></td> |
| <td class="data">20</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>-50</em></td> |
| <td class="data">50</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data">20</td> |
| <td class="data"><em>-20</em></td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>-10</em></td> |
| <td class="data">10</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>-40</em></td> |
| <td class="data">40</td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data">30</td> |
| <td class="data"><em>-30</em></td></tr> |
| <tr><th>lbstatus</th> |
| <td class="data"><em>0</em></td> |
| <td class="data">0</td></tr> |
| <tr><td class="data" colspan="3">(repeat)</td></tr> |
| </table> |
| |
| <p>That is after 10 schedules, the schedule repeats and 7 <var>a</var> |
| are selected with 3 <var>b</var> interspersed.</p> |
| </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="traffic" id="traffic">Weighted Traffic Counting Algorithm</a></h2> |
| |
| <p>Enabled via <code>lbmethod=bytraffic</code>, the idea behind this |
| scheduler is very similar to the Request Counting method, with |
| the following changes:</p> |
| |
| <p><dfn>lbfactor</dfn> is <em>how much traffic, in bytes, we want |
| this worker to handle</em>. This is also a normalized value |
| representing their "share" of the amount of work to be done, |
| but instead of simply counting the number of requests, we take |
| into account the amount of traffic this worker has seen.</p> |
| |
| <p>If a balancer is configured as follows:</p> |
| |
| <table><tr><th>worker</th> |
| <th class="data">a</th> |
| <th class="data">b</th> |
| <th class="data">c</th></tr> |
| <tr><th>lbfactor</th> |
| <td class="data">1</td> |
| <td class="data">2</td> |
| <td class="data">1</td></tr> |
| </table> |
| |
| <p>Then we mean that we want <var>b</var> to process twice the |
| amount of bytes than <var>a</var> or <var>c</var> should. It does |
| not necessarily mean that <var>b</var> would handle twice as |
| many requests, but it would process twice the I/O. Thus, the |
| size of the request and response are applied to the weighting |
| and selection algorithm.</p> |
| |
| </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="busyness" id="busyness">Pending Request Counting Algorithm</a></h2> |
| |
| |
| |
| <p>Enabled via <code>lbmethod=bybusyness</code>, this scheduler keeps |
| track of how many requests each worker is assigned at present. A new |
| request is automatically assigned to the worker with the lowest |
| number of active requests. This is useful in the case of workers |
| that queue incoming requests independently of Apache, to ensure that |
| queue length stays even and a request is always given to the worker |
| most likely to service it fastest.</p> |
| |
| <p>In the case of multiple least-busy workers, the statistics (and |
| weightings) used by the Request Counting method are used to break the |
| tie. Over time, the distribution of work will come to resemble that |
| characteristic of <code>byrequests</code>.</p> |
| |
| <p>This algorithm is available in Apache HTTP Server 2.2.10 and later.</p> |
| |
| </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> |
| <div class="example"><p><code> |
| <Location /balancer-manager><br /> |
| SetHandler balancer-manager<br /> |
| <br /> |
| Order Deny,Allow<br /> |
| Deny from all<br /> |
| Allow from .example.com<br /> |
| </Location> |
| </code></p></div> |
| |
| <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></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>. |
| 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 need 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> |
| <div class="example"><p><code> |
| ProxyPass /test balancer://mycluster stickysession=JSESSIONID|jsessionid scolonpathdelim=On<br /> |
| <Proxy balancer://mycluster><br /> |
| BalancerMember http://192.168.1.50:80 route=node1<br /> |
| BalancerMember http://192.168.1.51:80 route=node2<br /> |
| </Proxy><br /> |
| </code></p></div> |
| <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="../ja/mod/mod_proxy_balancer.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p> |
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