How to send a file/patch/message from IOT hub to IOT Edge device

Krithick Kalyan T 0

I want to upload a patch or Json file to the IOT Edge device from IOT hub.

I have connected the Edge device to the hub via DPS and have been able to send messages and trigger downloads from the hub from the Edge side using this. And I can send telemetry messages from Edge device to hub.

I did see it is possible to send messages to IOT devices but not IOT Edge devices. If i want to a message alerting the edge device to download or pushing the file from hub to the Edge device, how can i go for it?

I am using the Azure portal in the browser and not using the CLI or code for the IOT hub.

1 answer

Sander van de Velde | MVP 32,891 Reputation points MVP

2024-04-27T21:49:23.8166667+00:00
Hello @Krithick Kalyan T ,

welcome to this moderated Azure community forum.

You tell you use the Azure portal to manipulate devices registered within the Azure IoT Hub.

You have been able to connect an Edge device (a special kind of IoT Hub device) so you should understand it is build up in modules.

Where a regular 'direct internet connected' IoT device can be manipulated using its device twin (using eg. desired properties, reported properties, direct method, cloud message) an Azure IoT Edge device does not have these abilities.

It's the modules, each with their module twin that can be manipulated with their desired properties, reported properties, and direct methods.

So, if you want to send a file to an Azure IoT Edge device using the Azure IoT hub in the portal, you need to manipulate one of the modules running inside that edge device.

What you need is:

a (custom) module

access to the operating system for that module

a way to trigger a file download by the module

preventing cloud access to the file marked for download

I'm not aware if there are of-the-shelf modules available capable of reading a file from the cloud. I expect you need to write one yourself.

How can you send a file to a module?

Putting a file inside a desired property is not feasible due to the limited 32KB size available in a module twin.

A direct method can be used up to 128 KB.

I recommend putting the file in eg. an Azure Storage blob container and sending the file path over a desired property.

The module receives the module twin change event and downloads the file.

then, you need to provide your custom module access to the operating system because containers normally run 'sandboxed'.

This can be done with a 'bind' as seen in this blog post.

There is one more thing to think about, securing cloud access to the file.

You can provide the security credentials for the container in the desired properties. A better way is to use a SAS token for granting limited access to the file, living in the storage container.

I understand that there are quite a few steps needed before a file can be uploaded but this is how it can be done, at scale, for any size and secure.

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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Krithick Kalyan T 0 Reputation points

2024-05-01T05:15:18.5266667+00:00

Thanks for the answer @Sander van de Velde | MVP

I just need a bit more information regarding the answer for these parts, "sending the file path over a desired property. The module receives the module twin change event and downloads the file." Is there any links i could refer to try out these two parts?

If i need to release a patch i believe It will be done the same way?

Is this functionality of sending files, not complex in IOT central?

Sander van de Velde | MVP 32,891 Reputation points MVP

2024-05-01T07:16:00.89+00:00

Hello @Krithick Kalyan T ,

sorry for not being clear enough.

My answers describes how you can build this yourself.

These are standard Azure IoT Edge mechanism so you need some background experience. Because you already connected an Edge device I presumed you would understand it.

Check this for background info.

If a patch is updating a file, it works the way you program your module.

All intelligent logic is executed by the module. If Azure IoT Central is capable of manipulating module twins (desired properties of direct methods) you can do this with IoT Central too.

Krithick Kalyan T 0 Reputation points

2024-05-02T06:14:20.78+00:00

Hello @Sander van de Velde | MVP

I have already connected an Edge device as you have mentioned. Since i am new to this IOT edge and hub, I am bit overwhelmed. The link which you have tagged is for building a customized edge module. Is there any links for "sending the file path over a desired property" and for "module receives the module twin change event".

Are we talking about module twin or device twin? The edge devices do not have options to create a module identity. If I am wrong regarding this, please do share your insights and attached links.

Sander van de Velde | MVP 32,891 Reputation points MVP

2024-05-02T10:21:28.3266667+00:00

Hello @Krithick Kalyan T ,

no problem.

I recommend to first build up experience on how an Azure IoT Edge module works and interacts with the module twin. This is not a 'module Identity', that is a another concept.

Check out this training: https://learn.microsoft.com/en-us/training/modules/introduction-iot-edge/

The Device Twin is not relevant for Azure IoT. All interaction is done using the modules, the edge device and devicetwin is just a 'vehicle' to deploy and manage modules.

Modules are described and deployed with an edge deployment manifest.

Check the Set Modules dialog:

Desired properties can be set in the portal by editing JSON:

Here, an interval is set (ignore the metadata).

See this Azure IoT Edge module code example, reacting on the integer value.

You need to send the URL / path to the file (eg. stored in an Azure blob storage) with additional security.

Again, your usecase means you need to start programming to get this working in a scalable and flexible way.

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.

Krithick Kalyan T 0 Reputation points

2024-05-06T07:05:30.5266667+00:00

Hello @Sander van de Velde | MVP

I was able to check the module twin and direct methods under the IOT edge device.

I tried to invoke the direct method, I did get an error mentioning

The requested resource was not found. Details: The operation failed because the requested device isn't online or hasn't registered the direct method callback. To learn more, see https://aka.ms/iothub404103 Time (UTC): 2024-05-06T07:00:46.6545346Z Tracking ID: 955f82a39ef64a069d56b44ab9c977be-TimeStamp:05/06/2024 07:00:46

For the module twin method, how do I set up a module twin after selecting the set module button?

Is there a clearer explanation of the how the module twin change event works?

Sander van de Velde | MVP 32,891 Reputation points MVP

2024-05-06T17:55:38.1933333+00:00

Hello @Krithick Kalyan T ,

again, please start learning about cloud-to-device communication using the ModuleClient.

You try to invoke a DirectMethod on the ModuleClient so:

the device must be connected to the IoT Hub. It's a 'direct' method. The edge device and module must be accessible for the call from the cloud

Did you write custom code for the ModuleClient and it is listening for the calls?

Direct method calls are case-insensitive. So, 'ping' and 'Ping' are two different calls

Regarding the ModuleTwin, you can set the initial twin values using the twin settings:

Deploying a new deployment manifest just to update the twin values of one module is not the correct way.

You need to change Module Identity twin desired properties directly within the module:

The free MS Learn training modules and the Azure IoT Edge documentation is the way to go to do Azure IoT Edge the proper way.

Check this github repo as a starting point for eg. Direct Methods or a handler for processing twin changes.
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