Collectd Write MQTT plugin

The Write MQTT plugin sends the values collected by collectd to a MQTT broker. The data is formatted as JSON.

The plugin has beed developed and tested with version 5.7.

Configuration

Options

• Host: Hostname or IP-address of the MQTT broker.
• Port: Port number on which the MQTT broker accepts connections. Defaults to 8883.
• ClientId MQTT client ID to use. Defaults to the hostname used by collectd.
• CAPath Path to the PEM-encoded CA certificate file.
• ClientCert Path to the PEM-encoded certificate file to use as client certificate when connecting to the MQTT broker. Only valid if CAPath and ClientKey are also set.
• ClientKey Path to the unencrypted PEM-encoded key file corresponding to ClientCert. Only valid if CAPath and ClientCert are also set.
• Insecure Configure verification of the server hostname in the server certificate. Defaults to false.
• QoS Sets the Quality of Service. Defautls to 0.
• Topic Configures the topic to publish to. Defaults to collectd.
• StoreRates If set to true, convert counter values to rates. If set to false (the default) counter values are stored as is, i. e. as an increasing integer number.
• BufferSize Sets the send buffer size in Bytes. By increasing this buffer, less MQTT messages will be published, but more metrics will be batched / metrics are cached for longer before being sent, introducing additional delay until they are available on the server side. Bytes must be at least 1024 and cannot exceed 131072. Defaults to 131072.

Sample collectd.conf

LoadPlugin write_mqtt

<Plugin write_mqtt>
   <Node "sample">
     Host "mqtt.sample.com"
     CAPath "/path/to/root.ca.pem"
     ClientCert "/path/to/cert.pem"
     ClientKey "/path/to/private.key"
   </Node>
</Plugin>

Building

Copy src/write_mqtt.c into the collectd source and add following lines to the respective files:

• src/Makefile.am

  if BUILD_PLUGIN_WRITE_MQTT
  pkglib_LTLIBRARIES += write_mqtt.la
  write_mqtt_la_SOURCES = src/write_mqtt.c
  write_mqtt_la_CPPFLAGS = $(AM_CPPFLAGS) $(BUILD_WITH_LIBMOSQUITTO_CPPFLAGS)
  write_mqtt_la_LDFLAGS = $(PLUGIN_LDFLAGS) $(BUILD_WITH_LIBMOSQUITTO_LDFLAGS)
  write_mqtt_la_LIBADD = $(BUILD_WITH_LIBMOSQUITTO_LIBS) \
                      libformat_json.la
  endif
  

• configure.ac

  AC_PLUGIN([write_mqtt],          [$with_libmosquitto],      [MQTT json output plugin])
  

  AC_MSG_RESULT([    write_mqtt  . . . . . $enable_write_mqtt])