How to implement realtime Communication between Device and Azure Function over IoT Hub

Question

Hello,

i would like to implement a low-delay (near-realtime) control loop over Azure IoT Hub.
(I am aware of the problems and challenges of the time relevant control via the cloud)

Control Loop:
The microcontroller sends the current position of an actuator to the IoT Hub.

Input:
{"deviceId":"MyDevice","position_x":14.00,"position_y":24.00,"position_z":75.00}

The cloud service automatically execute a short calculation and send a response to the microcontroller with the new velocity.

Return:
{"deviceId":"MyDevice","velocity":3.00}

The service should run through this loop with a minimum of delay.

Current status:

As a first Step i created an IoT Hub and ran the given Quickstart-Examples (in python).
(https://learn.microsoft.com/en-us/azure/iot-hub/quickstart-send-telemetry-python)

In the next stage I used the MSP432E401Y Microcontroller from Texas Instruments instead of the SimulatedDevice.py.

After that I added Eventgrid + Azure Function.

Overview:

The Azure Function is in python and looks like:

function.json:

{  
    "scriptFile": "init.py",  
    "bindings": [  
    {  
         "type": "eventGridTrigger",  
         "name": "eventGridEvent",  
         "direction": "in"  
    }  
    ]  
}  

init.py:

 import json  
 import logging  
 import azure.functions as func  
 import datetime  
  
 import random  
 import sys  
 from azure.iot.hub import IoTHubRegistryManager  
      
 MESSAGE_COUNT = 1  
 AVG_WIND_SPEED = 10.0  
 MSG_TXT = "{\"service client sent a message\": %.2f}"  
      
 CONNECTION_STRING = "HostName=XXXX.azure-devices.net;SharedAccessKeyName=service;SharedAccessKey=XXXXX"  
 DEVICE_ID = "XXXX"  
      
 def iothub_messaging_sample_run():  
     try:  
         # Create IoTHubRegistryManager  
         registry_manager = IoTHubRegistryManager(CONNECTION_STRING)  
      
         for i in range(0, MESSAGE_COUNT):  
             print ( 'Sending message: {0}'.format(i) )  
             data = MSG_TXT % (AVG_WIND_SPEED + (random.random() * 4 + 2))  
      
             props={}  
             # optional: assign system properties  
             props.update(messageId = "Return_message_%d" % i)  
             props.update(correlationId = "correlation_%d" % i)  
             props.update(contentType = "application/json")  
      
             # optional: assign application properties  
             prop_text = "PropMsg_%d" % i  
             props.update(testProperty = prop_text)  
      
             registry_manager.send_c2d_message(DEVICE_ID, data, properties=props)  
      
     except Exception as ex:  
         print ( "Unexpected error {0}" % ex )  
         return  
     except KeyboardInterrupt:  
         print ( "IoT Hub C2D Messaging service sample stopped" )  
      
 def main(eventGridEvent: func.EventGridEvent) -> None:  
      
     result = json.dumps({  
         'id': eventGridEvent.id,  
         'data': eventGridEvent.get_json(),  
         'topic': eventGridEvent.topic,  
         'subject': eventGridEvent.subject,  
         'event_type': eventGridEvent.event_type,  
     })  
      
     logging.info('Python EventGrid trigger processed an event: %s', result)  
      
     iothub_messaging_sample_run()  
      
     msg_data = eventGridEvent.get_json()  
     logging.info(msg_data)  
          
     if 'properties' in msg_data and 'position' in msg_data['properties']:  
         logging.info(msg_data['properties']['position'])  

It works! But i am sure there is an easier or more efficient way to go (like Input + Output Binding in EventGrid). I tried it but didn't get it to work.

Question:
After I used the Provision Service to connect the device to cloud and used the authentication type "X.509 CA Signed" a "Connection String" isn't longer available.

Therefore my workaround over the connection string no longer work.

Could somebody explain me, how to fix it.

With best regards
Patrick

Answer 1

Hi @Patrick Schneider ,

I have limited experience with Python too.

I was able to get a Python Azure Function triggered:

the function.json looks like this:

{  
 "scriptFile": "__init__.py",  
 "bindings": [  
   {  
   "type": "eventHubTrigger",  
   "name": "events",  
   "direction": "in",  
   "eventHubName": "samples-workitems",  
   "connection": "mybeerliftconnection",  
   "consumerGroup": "pfa"  
   }  
 ]  
}  

in the portal:

The mybeerliftconnection references the public eventhub-compatible endpoint of the IoT hub:

Endpoint=sb://iothub-ns-[hidden].servicebus.windows.net/;SharedAccessKeyName=iothubowner;SharedAccessKey=[secret]=;EntityPath=beerlift-weu-ih  

It is stored in the application settings of the Azure Function App:

Answer 2

Hello @Sander van de Velde ,

I went through and understood the tutorials you linked. But things that should work according to the instructions still do not work.

Example:
https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-event-iot-trigger?tabs=python

The C# Script works fine, but when I do the same with the python example it doesn't work:
When I send data from a simulated device (10 Messages) in the C#-Function-App the Messages enter but in the python-Function-App no messages are arriving.

I am sure this should work:

JSON:
{
"scriptFile": "init.py",
"bindings": [
{
"type": "eventHubTrigger",
"name": "event",
"direction": "in",
"eventHubName": "samples-workitems",
"connection": "iot-XXXX-XXXX-001_events_IOTHUB",
"consumerGroup": "consumergroup-001"
}
]
}

Do you have any idea what the reason for this is?

Hope you could help me.

With best regards
Patrick