<!DOCTYPE html SYSTEM "about:legacy-compat">
<html lang="en"><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta content="width=device-width, initial-scale=1" name="viewport">
<!--
        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
              This file is generated from xml source: DO NOT EDIT
        XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
      -->
<title>mod_heartbeat - 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">
</script>

<link href="../images/favicon.png" rel="shortcut icon"></head>
<body>
<div id="page-header">
<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="https://cwiki.apache.org/confluence/display/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a> | <a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2">Report a bug</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="https://www.apache.org/">Apache</a> &gt; <a href="https://httpd.apache.org/">HTTP Server</a> &gt; <a href="https://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.4</a> &gt; <a href="./">Modules</a></div>
<div id="page-content">
<div id="preamble"><h1>Apache Module mod_heartbeat</h1>
<button aria-label="Toggle language list" class="lang-toggle"><svg xmlns="http://www.w3.org/2000/svg" stroke-width="2" stroke="currentColor" fill="none" viewBox="0 0 24 24" height="16" width="16"><circle r="10" cy="12" cx="12"/><line y2="12" x2="22" y1="12" x1="2"/><path d="M12 2a15.3 15.3 0 0 1 4 10 15.3 15.3 0 0 1-4 10 15.3 15.3 0 0 1-4-10 15.3 15.3 0 0 1 4-10z"/></svg></button>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_heartbeat.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../fr/mod/mod_heartbeat.html" hreflang="fr" rel="alternate" title="Fran&ccedil;ais">&nbsp;fr&nbsp;</a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Sends messages with server status to frontend proxy</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module&nbsp;Identifier:</a></th><td>heartbeat_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source&nbsp;File:</a></th><td>mod_heartbeat</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3 and later</td></tr></table>
<h3>Summary</h3>

<p> <code class="module"><a href="../mod/mod_heartbeat.html">mod_heartbeat</a></code> sends multicast messages to a <code class="module"><a href="../mod/mod_heartmonitor.html">mod_heartmonitor</a></code> listener 
that advertises the servers current connection count.  Usually, <code class="module"><a href="../mod/mod_heartmonitor.html">mod_heartmonitor</a></code>
will be running on a proxy server with <code class="module"><a href="../mod/mod_lbmethod_heartbeat.html">mod_lbmethod_heartbeat</a></code> loaded, which allows
<code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> to use the "heartbeat" <em>lbmethod</em> inside
of <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code>.</p>
<p>
    <code class="module"><a href="../mod/mod_heartbeat.html">mod_heartbeat</a></code> itself is loaded on the origin server(s) that serve requests 
    through the proxy server(s).  
</p>

    <div class="warning">
        To use <code class="module"><a href="../mod/mod_heartbeat.html">mod_heartbeat</a></code>,
        <code class="module"><a href="../mod/mod_status.html">mod_status</a></code> and <code class="module"><a href="../mod/mod_watchdog.html">mod_watchdog</a></code>
        must be either a static modules or, if a dynamic module, must
        be loaded before <code class="module"><a href="../mod/mod_heartbeat.html">mod_heartbeat</a></code>.
    </div>

</div>
<div id="quickview"><h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif"> <a href="#consuming">Consuming mod_heartbeat Output</a></li>
</ul><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif"> <a href="#heartbeataddress">HeartbeatAddress</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__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mod_heartbeat">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mod_heartbeat">Report a bug</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="section">
<h2 id="consuming">Consuming mod_heartbeat Output <a title="Permanent link" href="#consuming" class="permalink">&para;</a></h2>
    
  <p>
      Every 1 second, this module generates a single multicast UDP
      packet, containing the number of busy and idle workers.  The
      packet is a simple ASCII format, similar to GET query parameters
      in HTTP.
  </p>
  
<div class="example"><h3>An Example Packet</h3><p><code>
v=1&amp;ready=75&amp;busy=0
</code></p></div>

  <p>
    Consumers should handle new variables besides busy and ready,
    separated by '&amp;', being added in the future.
  </p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="heartbeataddress"><span id="HeartbeatAddress">HeartbeatAddress</span> Directive <a title="Permanent link" href="#heartbeataddress" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Multicast address for heartbeat packets</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>HeartbeatAddress <var>addr:port</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>disabled</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>Experimental</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_heartbeat</td></tr>
</table>
<p>The <code class="directive">HeartbeatAddress</code> directive specifies the
multicast address to which <code class="module"><a href="../mod/mod_heartbeat.html">mod_heartbeat</a></code> will send
status information. This address will usually correspond to a configured
 <code class="directive"><a href="../mod/mod_heartmonitor.html#heartbeatlisten">HeartbeatListen</a></code> on a
frontend proxy system.</p>
<pre class="prettyprint lang-config">HeartbeatAddress 239.0.0.1:27999</pre>
    

</div>
</div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/mod/mod_heartbeat.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../fr/mod/mod_heartbeat.html" hreflang="fr" rel="alternate" title="Fran&ccedil;ais">&nbsp;fr&nbsp;</a></p>
</div><div id="footer">
<p class="apache">Copyright 2026 The Apache Software Foundation.<br>Licensed under the <a href="https://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="https://cwiki.apache.org/confluence/display/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a> | <a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2">Report a bug</a></p></div><script><!--//--><![CDATA[//><!--
if (typeof(prettyPrint) !== 'undefined') {
    prettyPrint();
}
var langToggle = document.querySelector('.lang-toggle');
var topLang = document.querySelector('.toplang');
if (langToggle && topLang) {
    langToggle.addEventListener('click', function() { topLang.classList.toggle('open'); });
}
var qv = document.getElementById('quickview');
if (qv) {
    document.body.appendChild(qv);
    var qvBtn = document.createElement('button');
    qvBtn.className = 'qv-toggle';
    qvBtn.setAttribute('aria-label', 'Toggle page navigation');
    qvBtn.innerHTML = '&#9776;';
    document.body.appendChild(qvBtn);
    qvBtn.addEventListener('click', function() {
        var isOpen = qv.classList.toggle('open');
        if (isOpen) {
            qv.style.top = window.scrollY + 10 + 'px';
        }
    });
    window.addEventListener('scroll', function() { qv.classList.remove('open'); });
}
//--><!]]></script>
</body></html>