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petersaverman's avatar
petersaverman
Copper Contributor
Sep 07, 2020

Help understanding IoTHubDeviceClient in distributed modules

Hi,   I have a hard time wrapping my head around how to work with custom developed modules and connection strings. To make things easy, I've taken one of the Python scripts from the SDK examples on...
OlivierBloch's avatar
OlivierBloch
Former Employee
Sep 17, 2020

petersaverman the modules in IoT Edge do not need to authenticate with IoT Hub directly and you shouldn't use a device connection string nor the IoT HubDeviceClient  client in a module. As you have seen you need to use the IoTHubModule client.

The IoTEdge runtime is the one that will have to authenticate using the IoT Edge Device credentials created when provisioning in your IoT Hub(s). BTW I recommend using the Device Provisioning Service rather than connection strings when going to production. See some doc about this https://docs.microsoft.com/en-us/azure/iot-edge/how-to-auto-provision-x509-certs.

Once your IoT Edge devices connect and authenticate to the IoT Hub they were configured for, you can deploy the same module to multiple IoT Edge devices through IoT Hub using the https://docs.microsoft.com/en-us/azure/iot-edge/how-to-deploy-at-scale, the https://docs.microsoft.com/en-us/azure/iot-edge/how-to-deploy-cli-at-scale or your own code using the IoT Hub APIs.

Let me know if that puts you on the right track

 

 

petersaverman's avatar
petersaverman
Copper Contributor
Sep 22, 2020

OlivierBloch  

Thanks for responding and excuse my late reply. I've actually set up provisioning of my devices and that works fine. I did find a discussion regarding the IoTHubModuleClient not receiving a connection as well as not throwing an error under certain circumstances which I sadly can't remember now but this was my issue as well.

I'm trying to find out just how to use the IoTHubModuleClient to send a message to the Hub right now. Is that where the output comes in (via send_message_to_output) or do I still use the 

or should I still use the send_message method?

  • OlivierBloch's avatar
    OlivierBloch
    Former Employee
    Sep 22, 2020

    Hi petersaverman 

    The modules communication is enabled by the Edge Hub module which is part of the IoT Edge runtime. The idea is that  you configure routes between modules and up to the IoT Hub service at the IoT Edge runtime level and then in your module you can send messages to the output of the module defined in the routing configuration. You can learn more about the IoT Edge runtime concepts in https://docs.microsoft.com/en-us/azure/iot-edge/iot-edge-runtime#module-communication and more on the routing setup in https://docs.microsoft.com/en-us/azure/iot-edge/module-composition.

    If you want to send messages to IoT Hub directly from a module then you need to setup a route that takes all outputs from the module and sends to "upstream".

    For sending all messages from a specific module to IoT Hub, you would setup the route like this:

     

    "$edgeHub": {
    "properties.desired": {
        "routes": {
            "route1": "FROM /messages/modules/<moduleId>/* INTO $upstream"
        },
    }
}

     

     

    • petersaverman's avatar
      petersaverman
      Copper Contributor
      Sep 23, 2020

      OlivierBloch That is a totally different approach. From most example code there is embeded connection string which made me think that the modules sent the data themselves. Thanks for clarifying! Still, I tried another https://docs.microsoft.com/en-us/azure/iot-edge/tutorial-python-module and this still doesn't give me any messages when monitoring the endpoints. I'm starting to suspect that something else might be wrong. Is there a good approach to know where the fault is? Logs don't give anything away either. I expected the example above to "just work".

      • petersaverman's avatar
        petersaverman
        Copper Contributor
        Sep 23, 2020
        To clarify: the only output given from above mentioned example is:

        IoT Hub Client for Python
        The sample is now waiting for messages.
        Press Q to quit
        Press Q to quit
        Press Q to quit
        Press Q to quit
        ... and so on

        Nothing is triggered. Am I supposed to do something to trigger this?

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