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| <p class="apache">Apache HTTP Server Version 2.4</p> |
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| <div id="preamble"><h1>Apache Module mod_proxy_hcheck</h1> |
| <div class="toplang"> |
| <p><span>Available Languages: </span><a href="../en/mod/mod_proxy_hcheck.html" title="English"> en </a> | |
| <a href="../fr/mod/mod_proxy_hcheck.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p> |
| </div> |
| <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Dynamic health check of Balancer members (workers) for |
| <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></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_hcheck_module</td></tr> |
| <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_proxy_hcheck.c</td></tr> |
| <tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.4.21 and later</td></tr></table> |
| <h3>Summary</h3> |
| |
| <p>This module provides for dynamic health checking of balancer |
| members (workers). This can be enabled on a worker-by-worker |
| basis. The health check is done independently of the |
| actual reverse proxy requests.</p> |
| |
| <p>This module <em>requires</em> the service of <code class="module"><a href="../mod/mod_watchdog.html">mod_watchdog</a></code>.</p> |
| |
| <div class="note"><h3>Parameters</h3> |
| <p>The health check mechanism is enabled via the use of additional |
| <code class="directive"><a href="../mod/mod_proxy.html#balancermember">BalancerMember</a></code> parameters, which are configured |
| in the standard way via <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code>:</p> |
| |
| <p>A new BalancerMember <a href="mod_proxy.html#status_table">status</a> state (flag) |
| is defined via this module: "<code>C</code>". |
| When the worker is taken offline due to failures as determined by the health |
| check module, this flag is set, and can be seen (and modified) via the |
| <code>balancer-manager</code>.</p> |
| |
| <table> |
| <tr><th>Parameter</th> |
| <th>Default</th> |
| <th>Description</th></tr> |
| <tr><td>hcmethod</td> |
| <td>None</td> |
| <td>No dynamic health check performed. Choices are: |
| <table> |
| <tr><th>Method</th><th>Description</th><th>Note</th></tr> |
| <tr><td>None</td><td>No dynamic health checking done</td><td /></tr> |
| <tr><td>TCP</td><td>Check that a socket to the backend can be created: e.g. "are you up"</td><td /></tr> |
| <tr><td>OPTIONS</td><td>Send an <code>HTTP OPTIONS</code> request to the backend</td><td>*</td></tr> |
| <tr><td>HEAD</td><td>Send an <code>HTTP HEAD</code> request to the backend</td><td>*</td></tr> |
| <tr><td>GET</td><td>Send an <code>HTTP GET</code> request to the backend</td><td>*</td></tr> |
| |
| <tr><td colspan="3" /></tr> |
| <tr><td colspan="3">*: Unless <code>hcexpr</code> is used, a 2xx or 3xx HTTP status will be interpreted as <em>passing</em> the health check</td></tr> |
| </table> |
| </td></tr> |
| <tr><td>hcpasses</td> |
| <td>1</td> |
| <td>Number of successful health check tests before worker is re-enabled</td></tr> |
| <tr><td>hcfails</td> |
| <td>1</td> |
| <td>Number of failed health check tests before worker is disabled</td></tr> |
| <tr><td>hcinterval</td> |
| <td>30</td> |
| <td>Period of health checks in seconds (e.g. performed every 30 seconds)</td></tr> |
| <tr><td>hcuri</td> |
| <td> </td> |
| <td>Additional URI to be appended to the worker URL for the health check.</td></tr> |
| <tr><td>hctemplate</td> |
| <td> </td> |
| <td>Name of template, created via <code class="directive"><a href="#proxyhctemplate">ProxyHCTemplate</a></code>, |
| to use for setting health check parameters for this worker</td></tr> |
| <tr><td>hcexpr</td> |
| <td> </td> |
| <td>Name of expression, created via <code class="directive"><a href="#proxyhcexpr">ProxyHCExpr</a></code>, |
| used to check response headers for health.<br /> |
| <em>If not used, 2xx thru 3xx status codes imply success</em></td></tr> |
| </table> |
| </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="#examples">Usage examples</a></li> |
| </ul><h3 class="directives">Directives</h3> |
| <ul id="toc"> |
| <li><img alt="" src="../images/down.gif" /> <a href="#proxyhcexpr">ProxyHCExpr</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#proxyhctemplate">ProxyHCTemplate</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#proxyhctpsize">ProxyHCTPsize</a></li> |
| </ul> |
| <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_hcheck">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_proxy_hcheck">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><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="examples" id="examples">Usage examples</a></h2> |
| |
| |
| <p>The following example shows how one might configured health checking |
| for various backend servers:</p> |
| |
| |
| <pre class="prettyprint lang-config">ProxyHCExpr ok234 {%{REQUEST_STATUS} =~ /^[234]/} |
| ProxyHCExpr gdown {%{REQUEST_STATUS} =~ /^[5]/} |
| ProxyHCExpr in_maint {hc('body') !~ /Under maintenance/} |
| |
| <Proxy balancer://foo> |
| BalancerMember http://www.example.com/ hcmethod=GET hcexpr=in_maint hcuri=/status.php |
| BalancerMember http://www2.example.com/ hcmethod=HEAD hcexpr=ok234 hcinterval=10 |
| BalancerMember http://www3.example.com/ hcmethod=TCP hcinterval=5 hcpasses=2 hcfails=3 |
| BalancerMember http://www4.example.com/ |
| </Proxy> |
| |
| ProxyPass "/" "balancer://foo" |
| ProxyPassReverse "/" "balancer://foo"</pre> |
| |
| |
| <p>In this scenario, <code>http://www.example.com/</code> is health checked by sending a <code>GET /status.php</code> |
| request to that server and seeing that the returned page does not include the string <em>Under maintenance</em>. If |
| it does, that server is put in health-check fail mode, and disabled. This dynamic check is performed |
| every 30 seconds, which is the default.</p> |
| |
| <p><code>http://www2.example.com/</code> is checked by sending a simple <code>HEAD</code> request every |
| 10 seconds and making sure that the response status is 2xx, 3xx or 4xx. <code>http://www3.example.com/</code> is checked |
| every 5 seconds by simply ensuring that the socket to that server is up. If the backend is marked as |
| "down" and it passes 2 health check, it will be re-enabled and added back into the load balancer. |
| It takes 3 back-to-back health check failures to disable the server and move it out |
| of rotation. Finally, <code>http://www4.example.com/</code> is |
| not dynamically checked at all.</p> |
| |
| </div> |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="directive-section"><h2><a name="ProxyHCExpr" id="ProxyHCExpr">ProxyHCExpr</a> <a name="proxyhcexpr" id="proxyhcexpr">Directive</a></h2> |
| <table class="directive"> |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Creates a named condition expression to use to determine health of the backend based on its response</td></tr> |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ProxyHCExpr <em>name</em> {<em>ap_expr expression</em>}</code></td></tr> |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> |
| <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> |
| <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_proxy_hcheck</td></tr> |
| </table> |
| <p>The <code class="directive">ProxyHCExpr</code> directive allows |
| for creating a named condition expression that checks the response |
| headers of the backend server to determine its health. This named |
| condition can then be assigned to balancer members via the <code>hcexpr</code> |
| parameter.</p> |
| |
| <div class="example"><h3>ProxyHCExpr: Allow for 2xx/3xx/4xx as passing</h3><pre class="prettyprint lang-config">ProxyHCExpr ok234 {%{REQUEST_STATUS} =~ /^[234]/} |
| ProxyPass "/apps" "balancer://foo" |
| |
| <Proxy balancer://foo> |
| BalancerMember http://www2.example.com/ hcmethod=HEAD hcexpr=ok234 hcinterval=10 |
| </Proxy></pre> |
| </div> |
| |
| <div class="note"> |
| The <a href="../expr.html">expression</a> can use curly-parens ("{}") as |
| quoting deliminators in addition to normal quotes. |
| </div> |
| |
| <p>If using a health check method (eg: <code>GET</code>) which results in a response |
| body, that body itself can be checked via <code>ap_expr</code> using the <code>hc()</code> |
| expression function, which is unique to this module.</p> |
| |
| <p>In the following example, we send the backend a <code>GET</code> request |
| and if the response body contains the phrase <em>Under maintenance</em>, |
| we want to disable the backend.</p> |
| |
| <div class="example"><h3>ProxyHCExpr: Checking response body</h3><pre class="prettyprint lang-config">ProxyHCExpr in_maint {hc('body') !~ /Under maintenance/} |
| ProxyPass "/apps" "balancer://foo" |
| |
| <Proxy balancer://foo> |
| BalancerMember http://www.example.com/ hcexpr=in_maint hcmethod=get hcuri=/status.php |
| </Proxy></pre> |
| </div> |
| |
| <p><em>NOTE:</em> Since response body can quite large, it is best if used against specific status pages.</p> |
| |
| </div> |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="directive-section"><h2><a name="ProxyHCTemplate" id="ProxyHCTemplate">ProxyHCTemplate</a> <a name="proxyhctemplate" id="proxyhctemplate">Directive</a></h2> |
| <table class="directive"> |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Creates a named template for setting various health check parameters</td></tr> |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ProxyHCTemplate <em>name</em> <em>parameter</em>=<em>setting</em> [...]</code></td></tr> |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> |
| <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> |
| <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_proxy_hcheck</td></tr> |
| </table> |
| <p>The <code class="directive">ProxyHCTemplate</code> directive allows |
| for creating a named set (template) of health check parameters |
| that can then be assigned to balancer members via the <code>hctemplate</code> |
| parameter.</p> |
| |
| <div class="example"><h3>ProxyHCTemplate</h3><pre class="prettyprint lang-config">ProxyHCTemplate tcp5 hcmethod=tcp hcinterval=5 |
| ProxyPass "/apps" "balancer://foo" |
| |
| <Proxy balancer://foo> |
| BalancerMember http://www2.example.com/ hctemplate=tcp5 |
| </Proxy></pre> |
| </div> |
| |
| |
| </div> |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="directive-section"><h2><a name="ProxyHCTPsize" id="ProxyHCTPsize">ProxyHCTPsize</a> <a name="proxyhctpsize" id="proxyhctpsize">Directive</a></h2> |
| <table class="directive"> |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets the total server-wide size of the threadpool used for the health check workers</td></tr> |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ProxyHCTPsize <em>size</em></code></td></tr> |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ProxyHCTPsize 16</code></td></tr> |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr> |
| <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> |
| <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_proxy_hcheck</td></tr> |
| </table> |
| <p>If Apache httpd and APR are built with thread support, the health check |
| module will offload the work of the actual checking to a threadpool |
| associated with the Watchdog process, allowing for parallel checks. |
| The <code class="directive">ProxyHCTPsize</code> directive |
| determines the size of this threadpool. If set to <code>0</code>, no threadpool |
| is used at all, resulting in serialized health checks.</p> |
| |
| <div class="example"><h3>ProxyHCTPsize</h3><pre class="prettyprint lang-config">ProxyHCTPsize 32</pre> |
| </div> |
| |
| |
| </div> |
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