efrecon/mqtt-client repository overview

⁠MQTT Client

This minimal Alpine-based image⁠ contains the two mosquitto⁠ clients mosquitto_sub⁠ and mosquittto_pub⁠ for sending data to topics and subscribing to topics. The image exposes a volume at /opt/certs where CA certificates and/or client certificates can be placed for trusted communication to a remote server. However, the image also comes with the list of root certificates published by Mozilla, meaning that you should be able to connect to remote servers that are signed by one of the main authorities. The image⁠ is tagged⁠ according to the mosquitto releases contained in the successive Alpine releases. tags⁠ are built using a GitHub workflow⁠.

⁠Usage

The image exposes a volume at /opt/certs where CA certificates and/or client certificates can be placed for trusted communication to a remote server. However, the image also comes with the list of root certificates published by Mozilla, meaning that you should be able to connect to remote servers that are signed by one of the main authorities.

As the binaries are confined within a docker image, they are made accessible through the shorthands pub and sub at the command line (in addition to mosquitto_pub and mosquitto_sub). This allows for quicker interaction.

⁠Subscribing to Topics

The following command would listen to all topics at the test mosquitto server -v prints out the actual payload received:

docker run -it --rm efrecon/mqtt-client sub \
        -h test.mosquitto.org \
        -t "#" \
        -v

To connect to a TLS secure server, you could run a command similar to the one below instead:

docker run -it --rm efrecon/mqtt-client sub \
        -h iot.eclipse.org \
        -p 8883 \
        --capath /etc/ssl/certs \
        -t "#" \
        -v

⁠Publishing to Topics

To connect and publish data to topic test/testdevice something like this could be used

docker run -it --rm efrecon/mqtt-client pub \
        -h test.mosquitto.org \
        -p 1883 \
        -t "test/testdevice" \
        -m '[{"json":"validated","data":42},{"to":2,"test":"with"}]'

to publish more complex data from a file you need to mount access to local directories, e.g. passing ./datafile.json:

docker run -it --rm -v ${PWD}:/data/ efrecon/mqtt-client pub \
        -h test.mosquitto.org \
        -p 1883 \
        -t "test/testdevice" \
        -f /data/datafile.json

⁠Debugging

When problems occur, the -d for debug is recommended to see the connection information

In some systems it is important to provide a valid clientid to the MQTT server this can be done with -i specialclientid flag on the command-line.

⁠docker on MAC

This image need to now that it is runing on another platform to be able to run on a MAC OSX

 docker run --platform linux/amd64

⁠Technical Notes

The mosquitto code will not properly recognise the certificate bundles unless they are rehashed. This is achieved through calling /etc/ca-certificates/update.d/certhash as part of the image construction.

Clients can easily be interrupted from the command-line as they are placed behind tini through the entrypoint of the image.

Versioning follows the Alpine packages.