Sending big-sized messages to IoT hub, which pattern is architecturally correct?

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Sending big-sized messages to IoT hub, which pattern is architecturally correct?

Najam ul Saqib 440

Hi,I have an edge device sending a request to IoT hub having 10MB size (because it contains base64 images) but this will burn the daily quota at a higher rate.

I thought of uploading the images from edge device first to the blob and then sending URLs in message to IoT hub but this approach will require separate management of edge device's authentication with function app to get SAS URL

The other option is, since edge device is sending in the request to IoT hub what if I send one request first to IoT hub that gets redirected to logic/func app to return the SAS token and then device uploads and returns the urls to IoT hub hence decreasing message size. This will be done by communicating with IoT hub with same connection string hence no additional management overhead if this is even possible.

Which approach sounds scalable to you? Open to other ideas as well.

EDIT: I have just come to know that each message has to be under 256KBs sent to IoT hub, therefore direct sending is never an option forget about burning the daily quota, correct me if I am wrong.

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Answer 1

Sander van de Velde | MVP 36,941 MVP Volunteer Moderator

Hello @Najam ul Saqib ,

welcome to this moderated Azure community forum.

Sending blobs to the cloud via an IoT Hub is a bit of a challenge.

You will be charged in 4KB chunks with a maximum message size up to 256KB so 64 chunks.

Both options is feasible. You need access to a blob storage container which is probably not publicly available. So, sending a request from the edge to an Azure function behind the IoT Hub that generates a SAS token (limited in time) is a valid approach. Make sure you mark these technical flow messages with eg. application properties so you can route them on the IoT Hub to a separate flow, not mixed with regular messages.

An Event hub can only receive messages with a size up to 1 MB so this will not work in your case.

Still, did you check out this blob storage module from Microsoft?

It offers a smart way of copying files from the local disk to the cloud via Azure IoT Edge.

The only drawback is that the secrets of the storage is kept in the device twin. This is not directly readable on the device but some administrators are less knowledgeable with this approach of sending properties to the edge.

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.

Najam ul Saqib 440 Reputation points

2025-07-18T19:51:56.1266667+00:00

Is it correct that with 10MB request size I can't use IoT hub at all because it allows max 256KB size?

You mentioned event hub limit, what if I use service hub, does it also has some size limit?
Sander van de Velde | MVP 36,941 Reputation points MVP Volunteer Moderator

2025-07-20T18:40:29.5+00:00

Hello @Najam ul Saqib ,

You can use Azure IoT Edge because you are flexible with either custom code or the blob module.

Files are then send to eg. AzureStorage accounts.

The only change is that the IoT Hub communication itself does not support this size for Azure IoT Edge.

The standard IoT Hub communication accepts messages up to 256KB, and these are counted in 4KB chunks. If you can zip your 10MB files in less than 256KB, you can send the file as an IoT Hub message.

Because you have Azure IoT Edge, focus on those solutions.
Najam ul Saqib 440 Reputation points

2025-07-21T13:03:47.2833333+00:00
@Sander van de Velde | MVP Thank you, I'll utilize IoT edge's capability to upload images, it's a much better option. I have few more questions though:

Will I be able to fetch the URL of the uploaded file as I need to send it with the message to IoT hub for internal processing?

Since it's using IoT edge's capability to upload blobs, is it possible to use private endpoint between IoT hub and storage access and disable public access entirely to the storage account?
Sander van de Velde | MVP 36,941 Reputation points MVP Volunteer Moderator

2025-07-22T14:52:16.0933333+00:00

Hello @Najam ul Saqib ,

Regarding the first question, The upload functionality of the blob storage works like a data pump. You put a file on the local filesystem via custom code. That file is than picked up by the blob module and sent to the cloud.

Use the event mechanism of the cloud blob storage to process the files further on.

Check the blog post for details and try it out yourself.

Regarding the second question, I'm not sure if a it works without public access. The Azure IoT Edge is not aware of private endpoint, it needs access from the edge to the cloud. If you want to secure cloud communication from the edge, you probably need to set up a VNET / VPN solution covering both edge devices and cloud services. I did something like that in the past, check out this blog post.

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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Sending big-sized messages to IoT hub, which pattern is architecturally correct?

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