IOT Hub Multiple connections on single device

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IOT Hub Multiple connections on single device

Ben Dimelow 21

Background: We have multiple applications and windows services that run on our devices at any one time.
We were hoping we could communicate to IOT Hub from each of these services to send and receive messages but ran into this problem: https://learn.microsoft.com/en-us/azure/iot-hub/troubleshoot-error-codes#400027-connectionforcefullyclosedonnewconnection

Is there a way for multiple applications on a single device to each communicate to IOT hub at the same time?

If not what is the suggested practice for doing this?

Would we need to set up an app on the device for communicating with IOT and have each of our applications communicate through this?

This may add complexity and we wouldn't be able to report when this connection cannot be made.

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Answer 1

Sander van de Velde | MVP 36,766 MVP Volunteer Moderator

Hello @Ben Dimelow .

it seems you are reusing the same connection string for a single device multiple times.

Because the applications are bound to the same device, you obviously want to have single-device registration.

There are two ways to solve the 'collision'.

First, check out these module identities you can add to a single device:

Each module is a logical part of the device it is created in. It get's its own credentials:

Add a module identity for each application:

Now, the applications are still transmitting their messages as being part of that single device. Next to the DeviceId, the IoT Hub also exposes the ModuleId:

So, you can still distinguish the separate message 'source'.

The other solution is checking out Azure IoT Edge.

If your device is capable of running Docker containers (can it run Moby?) you could move your application logic into Docker containers and use Azure IoT Edge.

Actually, Azure IoT Edge registers these containers as modules too.

These are several advantages to checking out the edge.

In your case, there are two advantages seen as 'low hanging fruit':

modules messages bound for the cloud are stored automatically when the internet connection is not available. Messages are then sent at a later moment, no message loss or homebrew solution needed.
modules are updated from the cloud using the IoT Hub logic (a deployment manifest)

Ben Dimelow 21 Reputation points

2022-06-13T16:26:47.23+00:00

Thanks @Sander van de Velde | MVP for your response.

I've just been corrected by a member of my team. It is IOT Central that we are using at the moment, and the developer mentioned to me that he cannot see a way of creating module Identities in IOT Central.
Is this solution specific to IOT Hub or is there a similar mechanism in place if using IOT Central

Thanks,
Ben
Sander van de Velde | MVP 36,766 Reputation points MVP Volunteer Moderator

2022-06-13T19:19:05.827+00:00

Hello @Ben Dimelow ,

for as far as I have seen Azure IoT Central is not supporting modules on Azure IoT Devices.

Azure IoT Edge devices, complete with Azure IoT Edge modules, are supported though.

If needed you can give feedback here.
Alessandro Spadoni 0 Reputation points

2025-06-05T09:36:47.6466667+00:00
Hello, I understand a few years have passed but I hope you can help me as I have the very same issue. I am developing multiple modules in a single device with Azure Iot Hub and Azure Iot Edge.

For the first few development iterations I used the device connection string to establish the connection and it was working but now that I have two modules I can't reuse the same connection string (or even the secondary one as it is bound to the same device) and the connection is dropped.

How should I instantiate the IotHub client inside my modules to have both connected at the same time?

I need to be able to:

communicate with the hub with both modules

communicate inter-modules

If it helps, I am using the python sdk.

Thanks
Sander van de Velde | MVP 36,766 Reputation points MVP Volunteer Moderator

2025-06-06T07:45:41.36+00:00

Hello @Alessandro Spadoni ,

welcome to this moderated Azure community forum.

Please create a separate question if you want to proceed on the conversation because your question is based on Azure IoT Edge, not Azure IoT devices SDK.

In short, Azure IoT Edge has its own Azure IoT Hub identity and offers message buffering for messages coming from client modules when the cloud connection is interrupted.

Normally, each module sends it's own messages to the IoT Hub via that edge identity.

Still Azure IoT Edge can provide 'identity translation' but you need to build this yourself, and it is very uncommon (I have never seen in in dozens of projects).

If you need inter-module communication, the normal edge routing or direct methods work like a charm for this.

If you need communication with the hub for both modules, sending the messages to the iot hub via that edge connection and receiving module related direct methods and module twin related properties works like a charm.

Please check out the documentation on how to use Azure IoT Edge modules as-is.

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IOT Hub Multiple connections on single device

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