/Apache HTTP Server

Apache Module mod_heartbeat

Description: Sends messages with server status to frontend proxy
Status: Experimental
ModuleIdentifier: heartbeat_module
SourceFile: mod_heartbeat
Compatibility: Available in Apache 2.3 and later


mod_heartbeat sends multicast messages to a mod_heartmonitor listener that advertises the servers current connection count. Usually, mod_heartmonitor will be running on a proxy server with mod_lbmethod_heartbeat loaded, which allows ProxyPass to use the "heartbeat" lbmethod inside of ProxyPass.

mod_heartbeat itself is loaded on the origin server(s) that serve requests through the proxy server(s).

To use mod_heartbeat, mod_status and mod_watchdog must be either a static modules or, if a dynamic module, must be loaded before mod_heartbeat.

Consuming mod_heartbeat Output

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.

An Example Packet


Consumers should handle new variables besides busy and ready, separated by '&', being added in the future.

HeartbeatAddress Directive

Description: Multicast address for heartbeat packets
HeartbeatAddress addr:port
Default: disabled
Context: server config
Status: Experimental
Module: mod_heartbeat

The HeartbeatAddress directive specifies the multicast address to which mod_heartbeat will send status information. This address will usually correspond to a configured HeartbeatListen on a frontend proxy system.


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Licensed under the Apache License, Version 2.0.