Filtering EventGrid Topic MQTT Messages

Question

Filtering EventGrid Topic MQTT Messages

Mark Pope 50

I need to subscribe to an external MQTT broker and publish MQTT messages received from the Azure Event Grid. I created a Function App that triggers on MQTT messages. The function app must interrogate each message and call one of several MQTT clients based on who should receive the topic. With decoding this seems like an inefficient solution. Another solution is to have Function app subscribe to Event Grid topic spaces as MQTT clients, allowing them to collect the correct topics and publish to appropriate clients(brokers). Thoughts?

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Answer 1

Sander van de Velde | MVP 36,146 MVP

Hello @Mark Pope ,

welcome to this moderated Azure community forum.

It seems you want to have this architecture:

External MQTT broker <- Some client in an Azure Function checking each message and picking the right topic to publish to-> EventGrid Namespace MQTT Broker <- One or more possible clients listening to topics

Function apps are stateless and not suitable for long running services (listening as a subscriber for messages). It also means constant connect/disconnect.

One way to overcome this is to move over to an Azure Container Instance because it is stateful.

Check out this example with code. In this case, it reads messages from an Azure EventHub but the blue print should help you with building a stable solution.

If the response helped, do "Accept Answer". If it doesn't work, please let us know the progress. All community members with similar issues will benefit by doing so. Your contribution is highly appreciated.

Mark Pope 50 Reputation points

2025-04-23T22:38:38.56+00:00

@Sander van de Velde | MVP Thanks for that! I wasn't aware of container instances. My function app uses an async client and did quite well keeping up with the load but I see that its stateless is not reliable. I'll read up and move my code to a container.

My data flow is:

1.

mqtt devices -> Event Grid <- external clients subscribing

2.

mqtt devices -> Event Grid ->Event Grid Topic <-(Container Instance - mqtt client publishing)-> external mqtt broker

I need to deploy several container instances for different topic consumers. Should I use an mqtt client in the Container to subscribe to Event Grid? This would allow me to utilize Topic Space filtering instead of filtering in each container instance.
Sander van de Velde | MVP 36,146 Reputation points MVP

2025-04-24T06:06:12.83+00:00

Hello @Mark Pope ,

I prefer connecting devices via topics directly so yes, an MQTT client is needed. See the code example on how to connect.

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Filtering EventGrid Topic MQTT Messages

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