How to publish an MQTT message in Event grid after the reception of a message in Event Hub ?

Omar Cruz 21

Hello.
My devices report the data by MQTT, messages easily received in event grid.

Event grid passes the messages to Event Hub.

Event hub passes the messages where there are treated, filtered, etc.

The response is sent back to Event Hub.

From Event Hub these messages received should now be passed to Event Grid (so they can be published as MQTT messages) and this is where I am not very sure how to proceeed. Would you have any ideas? I have checked all the documentation but still I don't find my way...

Thanks in advance for any assistance.

Omar C.

PRADEEPCHEEKATLA-MSFT 90,146 Reputation points Microsoft Employee

2024-07-22T05:08:19.7133333+00:00

@Omar Cruz - Just checking in to see if the below answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

1 answer

Sander van de Velde | MVP 32,736 Reputation points MVP

2024-07-15T15:21:34.2+00:00

Hello @Omar Cruz,

welcome to this moderated Azure community forum.

You make use of routing MQTT messages towards an Eventhub:

This is a one-way connection, from MQTT broker towards Azure services.

If you need to send message on certain topics, you need to create a separate MQTT client for sending these messages.

Because you need to create a client connection before sending messages, a stateful client is recommended so the connection is kept alive.

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.
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Omar Cruz 21 Reputation points

2024-07-16T09:49:34.37+00:00

Hello @Sander van de Velde | MVP !

Yes, I am just getting familiar with this community forum and it looks great ! It is very nice to see how much people can help to each other.

1.1 I have some devices reporting in MQTT (temperature, etc), these MQTT messages are being sent to the MQTT Broker of event grid.

1.2 These events are then passed from event grid to event hub

1.3 Event hub passes these 'events' to Stream Analytics where the events are treated. The events have a property called 'data_base64', where the information that I need (temperature, etc) is located.

I do a bit of manipulation on the temp values (to filter or correct worng values like extremely high or low temperatures, etc) then I need to send this back to the device as 'corrected_value', so my idea was:

2.1 In azure stream analytics, I define the Event Hub as output.

2.2 From Event hub I pass it to Event Grid

2.3 Event grid publishes the event as an MQTT Message... All is ok :)

Steps 1.1, 1.2 and 1.3 are fine 👌

The challenge is more on the step 2.2: We haven't found any documentation showing how can I send the events from Event Hub to Event Grid...

If @Richar Sosa and me could find or have any ideas about this, it would be great :)

Thanks a lot for sharing your experiences with us.

Sander van de Velde | MVP 32,736 Reputation points MVP

2024-07-16T16:17:29.65+00:00

Hello @Omar Cruz,

It seems not possible to automatically send a message to a MQTT client via 'Event Hub to Event Grid' or an Event Grid Topic. There is no MQTT destination. It's also not clear how the MQTT topics are limited.

To send a message from the Stream Analytics job to the MQTT broker in the EventGrid, you need to create some piece of logic, custom code, reacting on the ASA message and sending it as a MQTT Client running in the cloud.

This could eg. be an Azure Function ingesting the ASA message.

Please check out Web App WebJobs because these stateful.

(durable functions are also documented as being stateful but that is more like a finite state machine approach of remembering state). A Docker container running in ACS or a VM could do the job too...
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