MQTTKit application#


A generic distributed monitoring platform for collecting sensor data in wide area network setups and multi-node, multi-sensor environments ¹.

It emphasizes MQTT as communication protocol and JSON as data serialization format but implements different other protocols and formats.


Application section#

The core of each data acquisition application is its configuration object. The file etc/examples/mqttkit.ini can be used as a configuration blueprint.

This configuration snippet will create an application object defined as [mqttkit-1].

 1; ------------------------------------------
 2; Name:     mqttkit
 3; About:    A generic distributed monitoring platform for
 4;           collecting sensor data in wide area network setups.
 5; Channel:  Transport: MQTT over TCP; Format: JSON
 6; Storage:  InfluxDB
 7; See also:
 8; ------------------------------------------
11enable      = true
12type        = application
13realm       = mqttkit-1
14mqtt_topics = mqttkit-1/#
15application = kotori.daq.application.mqttkit:mqttkit_application

Multiple MQTT brokers#

It is possible to make Kotori connect to an individual MQTT broker per application. On behalf of this example, you would create a separate configuration section [mqttkit-1:mqtt], where mqttkit-1 reflects the value of the realm attribute of the main application settings section.

 2enable      = true
 3type        = application
 4realm       = mqttkit-1
 5mqtt_topics = mqttkit-1/#
 6application = kotori.daq.application.mqttkit:mqttkit_application
 8# How often to log metrics
 9metrics_logger_interval = 60
11# Restrict SensorWAN direct addressing to specified networks/owners.
12direct_channel_allowed_networks = itest, testdrive
14# [mqttkit-1:mqtt]
15# ; Configure individual MQTT broker for this application.
16# ; The option group prefix `mqttkit-1` reflects the value of
17# ; the `realm` attribute of the application settings.
18# host        =
19# port        = 1883
20# username    = foobar
21# password    = secret


Wide channel#

To successfully publish data to the platform, you should get familiar with the MQTTKit addressing scheme. We call it the »quadruple hierarchy strategy« and it is reflected on the mqtt bus topic topology.

The topology hierarchy is made up of four identifiers:

realm / network / gateway / node

The realm will be configured within the server configuration file while all other parameters designate the data acquisition channel and can be assigned by the user.

The topology identifiers are specified as:

  • “realm” is the designated root realm. You should prefix the topic name with this label when opting in for all features of the telemetry platform.

  • “network” is your personal realm, it designates the owner. Choose anything you like or use an Online UUID Generator to gain maximum uniqueness.

  • “gateway” is your gateway identifier, it designates a sensor node location or group. Choose anything you like.

  • “node” is your node identifier. Choose anything you like. This usually gets transmitted from a sensor device.

In the following examples, this topology address will be encoded into the variable CHANNEL.

Direct channel#

When using the Direct addressing scheme of SensorWAN 3.0, it is possible to detour from the “wide” addressing scheme, and submit data “directly” to a channel address like mqttkit-1/channel/<network>-<gateway>-<node> instead.

In order to restrict access to that addressing flavour to specific networks/owners only, you can use the direct_channel_allowed_networks configuration setting, where you can enumerate network/owner path components, which are allowed to submit data on their corresponding channel groups.

1# Restrict SensorWAN direct addressing to specified networks/owners.
2direct_channel_allowed_networks = itest, testdrive

For all others, access will be rejected by raising an ChannelAccessDenied exception.

Direct device#

The Direct addressing scheme also allows you to address channels by device identifiers only, also detouring from the “wide” addressing scheme.

An example for a corresponding channel address, identifying devices by UUID, would be

Sending data#

In the following examples, the topology address will be encoded into the variable CHANNEL.

# Define channel and data.
DATA='{"temperature": 42.84, "humidity": 83.1}'

# Publish telemetry data to MQTT topic.
echo "$DATA" | mosquitto_pub -t $CHANNEL/data.json -l

When using the “direct channel” addressing scheme, those invocations would address the same channel as in the previous example:

echo "$DATA" | mosquitto_pub -t $CHANNEL/data.json -l

Receiving data#

# Receive telemetry data by subscribing to MQTT topic
mosquitto_sub -t mqttkit-1/#

¹ The design of MQTTKit is derived from vendor Hiveeyes.