How to route Azure IOT hub messages to Event Grid MQTT broker

Hello @Dylan Yeo ,

in all scenarios, you need to put custom logic (like an Azure function) behind the IoT Hub to route messages between services.

You need to route IoT Hub device messages to the other service first. You also need to listen for messages coming from that other service and send them to the device(s) of your choice.

The Azure IoT Hub has a route towards EventGrid but this supports the classic one-way EventGrid publisher/subscriber pattern only.

This does not connect to the new MQTT Broker feature of EventGrid.

So you must add extra d2c and c2d communication logic for this solution too.

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https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-messages-d2c

Azure doesn't have built-in support for routing IoT Hub messages directly to an external MQTT broker. You would need to create an intermediary service (like an Azure Function or Logic App) to act as a bridge.

But

Azure IoT Hub can be integrated with Event Grid to enable powerful and complex routing rules.

https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-event-grid

Hi @Dylan Yeo You can route the events from Azure IoT Hub to an Event Hub. You can then create an Azure function that triggers based on the Event hub data and send the data to Mosquitto MQTT end point through the function. Here is a sample function for your reference.

using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using MQTTnet;
using MQTTnet.Client;
using System;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace MosquittoPublisher
{
    public static class MosquittoPublisherFunction
    {
        private static readonly Lazy<IMqttClient> lazyMqttClient = new Lazy<IMqttClient>(() =>
        {
            var factory = new MqttFactory();
            var client = factory.CreateMqttClient();

            var options = new MqttClientOptionsBuilder()
                .WithTcpServer("localhost", 1883)
                .Build();

            client.ConnectAsync(options, CancellationToken.None).Wait();

            return client;
        });

        private static IMqttClient MqttClientInstance => lazyMqttClient.Value;

        [FunctionName("MosquittoPublisherFunction")]
        public static async Task Run(
            [EventHubTrigger("myeventhub", Connection = "EventHubConnection")] EventData[] eventHubMessages,
            ILogger log)
        {
            foreach (var message in eventHubMessages)
            {
                var mqttMessage = new MqttApplicationMessageBuilder()
                    .WithTopic("test/topic")
                    .WithPayload(message)
                    .WithRetainFlag()
                    .Build();

                await MqttClientInstance.PublishAsync(mqttMessage, CancellationToken.None);
            }
        }
    }
}

Please make sure to provide the correct hostname and the port in the options variable to point to your Mosquitto MQTT broker.

Here is a code sample in Python.

import logging
import azure.functions as func
import paho.mqtt.client as mqtt

# Define the MQTT broker address and port
broker_address = "localhost"
broker_port = 1883

# Create an MQTT client and connect to the broker
client = mqtt.Client()
client.connect(broker_address, broker_port)

app = func.FunctionApp()

@app.function_name(name="EventHubTrigger1")
@app.event_hub_message_trigger(arg_name="myhub", 
                               event_hub_name="<EVENT_HUB_NAME>",
                               connection="<CONNECTION_SETTING>") 
def test_function(myhub: func.EventHubEvent):
    # Get the body of the Event Hub event
    event_body = myhub.get_body().decode('utf-8')

    # Define the topic and message to send
    topic = "test/topic"
    message = event_body

    # Publish the message to the broker
    client.publish(topic, message)

    # Log a message to the Azure Function log
    logging.info('Python EventHub trigger processed an event: %s', event_body)

    # Disconnect from the broker
    client.disconnect()

Here is a sample response I have received when I subscribed to my local MQTT topic on my local machine.

Please find the following resources that will help you with the routing and creation of Azure function.

• Create Routes from IoT Hub to Event Hub
• Azure Event Hubs trigger for Azure Functions

Hope this helps. Please let us know if you have any additional questions.

If the response helped, please do click Accept Answer and Yes for the answer provided. Doing so would help other community members with similar issue identify the solution. I highly appreciate your contribution to the community.