MQTT broker

An on-site MQTT broker, for all of your real-time data

MQTT is a pub-sub protocol for real-time data, popular in IoT and embedded scenarios because of how lightweight it is.

In MQTT, a “broker” is basically a server that you connect to, in order to read (subscribe) or write (publish) data on named topics. A topic has a name (such as emf/ducks)and a set of clients which are subscribed to it at any point in time.

After running a slightly undersold MQTT broker in 2022, the Networks team (NOC) are making more of an effort in 2024. We would love to see what you can share with the field over MQTT.

MQTT doesn’t place any restrictions on what you send in payloads to a given topic. It could be UTF-8 text, JSON, or a binary message! Make sure you publish your data in a format that’s relatively easy to consume, though :)

Server connection details

Hostname: mqtt.emf.camp

Ports available:

  • 1883, no TLS (plaintext)
  • 8883, with TLS (encrypted)

You don’t need to authenticate.

Topics and permissions

Unauthenticated clients can publish (write) and subscribe (read) on any topic name, except topics beginning with emf/, which are reserved for specific event purposes.

We use the topics under emf/ to help run the event! That said, we also want to share all the data we can. Unauthenticated clients can subscribe to any of the emf/ topics, but we just have to stop the world from being able to inject dodgy data in.

Known topic namespaces

Check out topics with these prefixes, which might have something fun to look at:

  • emf/bar/ – live stats from the Robot Arms and Null Sector’s Cybar. See the Bar page for the full rundown of what’s published here.
    TL;DR: anything available over the websocket API is also going to be on MQTT.
  • emf/films/ – EMF Films will be publishing “an unnecessary level of info” under here.
  • emf/weather/ – live weather data from HQ. Full details on the Weather page.

Tips on topic naming, and wildcard subscriptions

Topics are best named hierarchically, because MQTT supports subscribing to entire groups of topics at once using wildcards.

For example, you could subscribe to all the EMF Films data with one subscription to emf/films/#. The # wildcard works much like how an asterisk – * – works outside of MQTT, like in typical filename wildcards, but it can only appear at the end of a subscription.

There is also a + wildcard, which works at a single topic ’level’, that is, a bit of a topic name between slashes. For example, subscribing to emf/fauna/+/count would subscribe to both emf/fauna/ducks/count and emf/fauna/spiders/count – if those topics existed ;)

Here is some further reading on MQTT topic names and wildcard subscriptions: https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices/

Last modified May 25, 2024: Crosslink between MQTT and Weather pages (44ecad4)