MQTT-ST: a Distributed Mosquitto Evolution

MQTT-ST is a MQTT broker which is able to create a distribute architecture of brokers, organized thorugh a spanning tree. It based on the open source Mosquitto broker implementation. Our version mainly adds a feature for interconnecting MQTT brokers automatically in a loop-free topology. Other Mosquitto features remain inalterated.

Links

See the following links for more information on MQTT-ST:

• IEEE paper: https://ieeexplore.ieee.org/document/9149046
• Arxiv paper: https://arxiv.org/pdf/1911.07622.pdf
• Source code Mosquitto repository: https://github.com/eclipse/mosquitto
• Source code repository: https://github.com/edoardesd/mosquitto

Creator information is available at the following locations:

• Research group webpage: http://www.antlab.polimi.it
• Developer github: https://github.com/edoardesd

Installing

Installing MQTT-ST is as installing Mosquitto. See the official documentation at https://mosquitto.org/download/ for details on installing binaries for various platforms.

Installing on MacOSX

• mkdir build
• cd build
• cmake -DCMAKE_C_COMPILER=/Library/Developer/CommandLineTools/usr/bin/cc -DCMAKE_CXX_COMPILER=/Library/Developer/CommandLineTools/usr/bin/c++ -DCMAKE_SYSTEM_NAME=Darwin -DOPENSSL_ROOT_DIR=/usr/local/opt/openssl -DWITH_TLS=OFF -DDOCUMENTATION=OFF ..
• make install

It is important to set the correct C compiler and disable TLS.

XCode setup (for developer)

• Set in the External Build Tool Configuration:
  • Build Tool: /usr/local/bin/cmake
  • Arguments: the cmake arguments (.. included)
  • Directory with build
  • [ x ] Pass build settings in environment
• Enable automatic make install
  • Edit Run Scheme
  • Executable: bash (in /bin folder)
  • Arguments passed on launch: -c "make install"
  • Options: use custom working directory (build directory)

Cluster quick start

Also the quick start for a single broker is the same as Mosquitto. More information at: https://github.com/eclipse/mosquitto#quick-start.

If you want to create a cluster of brokers, each broker must be spawned manually with a valid configuration file, i.e. mosquitto -c mosquitto.conf

Configuration file

MQTT-ST provides a mechanism for interconnecting automatically Mosquitto brokers in a loop free fashion. It is based on the bridging feature provided by Mosquitto (https://mosquitto.org/man/mosquitto-conf-5.html).

The bridges are created through the mosquitto.conf file. Every broker in the cluster must have a valid configuration file. The file includes a valid bridge to all the others brokers in the cluster. It consists in:

• arbitrary connection name
• broker destination address
• broker destination port (if different to the default port 1883)
• topic included in the cluster
• topic forwarding option: it must be out for ensuring the correct behaviour. See https://mosquitto.org/man/mosquitto-conf-5.html for more details
• QoS option: high QoS is suggested
• remote broker id: anyone

Example

Here we show an example of a cluster composed by MQTT-ST brokers. For the sake of simplicity, only 3 brokers are used: A, B and C. However, MQTT-ST can support as many brokers as your machine can start.

Every broker in the cluster must be bridged to every one else. Each broker has a different .conf file containing bridges towards all the others brokers.

For instance, broker A configuration file:

connection AtoB
address 192.168.1.3:1883
topic # out 2
remote_clientid AtoB

connection AtoC
address 192.168.1.4:1883
topic # out 2
remote_clientid AtoC

Broker C configuration file:

connection BtoA
address 192.168.1.2:1883
topic # out 2
remote_clientid BtoA

connection BtoC
address 192.168.1.4:1883
topic # out 2
remote_clientid BtoC

And so on...

Future works

• Develop a script which creates valid configuration files
• Automatic discovery of MQTT-SN brokers
• Create a tree for each topic in the system