MQTT for Elixir

The article presents MQTT as an alternative to HTTP for embedded and IoT communication in Elixir. It explains the broker-based pub/sub model, then builds a simple sensor application that publishes temperature readings and listens for interval changes.

Reading notes

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• MQTT is described as a messaging protocol for device communication, using a lightweight binary protocol over TCP/IP and fitting unreliable networks.
• The protocol uses pub/sub, so clients connect to a broker instead of a server.
• A broker such as EMQX can also offer WebSockets, authentication and authorization, streaming to databases, and custom routing rules.
• The sensor example is an ordinary Mix application that can be turned into a Nerves app.
• The sensor module starts an MQTT client, subscribes to commands/#{clientid}/set_interval, and schedules periodic ticks.
• On each tick, it generates a {Timestamp, Temperature} tuple and publishes it to reports/#{clientid}/temperature.
• The dashboard is a Phoenix LiveView app that also acts as an MQTT client.
• It subscribes to reports/# and publishes interval commands to commands/#{id}/set_interval.
• Incoming temperature reports are converted into a chart rendered with Contex.
• The form on the dashboard sends a new interval to the device topic and updates the charting process state.
• The article notes that retained command messages let a restarted device receive the last configured interval on reconnect.