How to restrict and alert the user when they upload a file size of greater than xx MB's on ADLS Gen2 account

Question

How to restrict and alert the user when they upload a file size of greater than xx MB's on ADLS Gen2 account

manigandan 0

Hello Team

I'm working on couple of requests:

I wanted to restrict and alert the user when they are trying to upload a file of given threshold size. (Say > 50MB)
I wanted to restrict and alert the user when they are trying to upload a file of irrelevant extension types (which is not whitelisted from the team)

We are using MS Storage Explorer with the SAS token to upload the files to the ADLS containers.

I've searched multiple articles and forums for any workaround. I couldn't get any, could someone help here. Your help is much appreciated.

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Answer 1

Alex Burlachenko 1,755

Hi,

U can use Azure Event Grid and Azure Functions

Set up an Event Grid subscription for the Blob Created event on your ADLS Gen2 account. This will trigger whenever a file is uploaded. Refer to the Event Grid documentation. Create an Azure Function to process the event. The function will check the file size using the Content-Length property.

If the file exceeds the threshold (e.g., 50MB), send an alert (e.g., via email using Logic Apps or an alerting service) and optionally delete the file. Refer to the Azure Functions documentation.

Best regards, Alex p.s. If you found the answer helpful, please click on Upvote and Accept Answer. This will help other community members.

manigandan 0 Reputation points

2025-03-11T14:42:20.3533333+00:00

Hi @Anonymous

Thanks for your response. Is there anyway to do while upload the file rather than doing the validation after uploaded the file to Storage account?
Alex Burlachenko 1,755 Reputation points

2025-03-11T14:55:08.03+00:00

Hi again,
so as i know currently, Azure Data Lake Storage Gen2 (ADLS Gen2) does not provide built-in mechanisms to preemptively restrict uploads based on file size or extension within Azure Storage Explorer. But... as usually u can play arround.
Using Azure Storage REST API / SDK if you control the upload process (e.g., using Python, .NET, or another SDK), you can implement client-side validation before sending the file, I would do it this way, but these are "workarounds," not out-of-the-box features. Check file size before upload. Validate the file extension against a whitelist. Block the upload if it does not meet the criteria.

Azure Storage Account SAS Token with Limited Permissions. Since you're using SAS tokens, there's no direct way to restrict file size or extensions within the token itself. However, you can implement an upload proxy (via Azure Function or API Gateway) that validates the file before generating a SAS token. Allow uploads only through a controlled interface instead of direct access via Storage Explorer. Azure Storage Firewall & Policies (Indirect Approach). You can use Azure Policy to audit and detect non-compliant uploads, but not to block uploads in real-time. Azure Defender for Storage can monitor and alert on suspicious activity but does not enforce pre-upload restrictions.

Event Grid & Azure Function (Post-Upload Validation). This is the most common approach used in Azure. An Event Grid trigger detects file uploads and invokes an Azure Function that checks the file size and type. If a file is too large or has an invalid extension, the function can delete the file and notify users.

again I would do it this way, but these are "workarounds," not out-of-the-box features really... probably it would work, may be not, need to check...

rgds,

Alex
Vinod Kumar Reddy Chilupuri 3,035 Reputation points Microsoft External Staff

2025-03-12T14:40:01.35+00:00

Hi manigandan,
Just checking in to see if the provided answer helped. If this answers your query, do click "Accept the answer” for the same, which might be beneficial to other community members reading this thread. And, if you have any further queries do let us know.

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How to restrict and alert the user when they upload a file size of greater than xx MB's on ADLS Gen2 account

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