Apache HTTP Server Version 2.4

Apache > HTTP Server > Documentation > Version 2.4 > Modules

# Apache Module mod_heartbeat

Description: | Sends messages with server status to frontend proxy
Status: | Experimental
Module Identifier: | heartbeat_module
Source File: | mod_heartbeat
Compatibility: | Available in Apache 2.3 and later

### Summary

`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`.

### Topics

- Consuming mod_heartbeat Output

### Directives

### Bugfix checklist

- httpd changelog
- Known issues
- Report a bug

## 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

`v=1&ready=75&busy=0`

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

## HeartbeatAddress Directive

Description: | Multicast address for heartbeat packets
Syntax: | `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.

    HeartbeatAddress 239.0.0.1:27999