Temp directory files persistence in Azure Functions

Question

Temp directory files persistence in Azure Functions

HKPR 41

Listened that the file uploaded to the temp directory when running the azure functions, gets deleted automatically.
When I ran the function in the same session each time, the files are in the temp directory for each run - why they are being available for each run, they should get deleted but not?

If they are not deleted, any security issues when files are in that temp directory because consumption plans mean sharing resources.

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Answer 1

MughundhanRaveendran-MSFT 12,506

Hi @HKPR ,

Thanks for reaching out to Q&A.

The files present in the Temp directory are temporary files, they are deleted automatically once in 12 hours (not after each run) or if the app is restarted. Unlike Persisted files, these files are not shared among site instances. Also, you cannot rely on them staying there. So there are no security issues concerned here.

Please look into this article for more details: https://github.com/projectkudu/kudu/wiki/Understanding-the-Azure-App-Service-file-system#temporary-files

Hope this helps! Feel free to reach out to me if you have any queries or concerns.

Haris Qureshi 0 Reputation points

2024-08-23T09:43:43.07+00:00

Hi,
Thanks for the information, please if you can also clarify that if all the files present in the temp directory are deleted, or only the ones which are 12 or more hours older?

Thanks.
Bilal Hussain Shah 0 Reputation points

2024-08-23T14:46:50.2933333+00:00

Hi @MughundhanRaveendran-MSFT

Can you please confirm if the clean-up of the files are based on some filters like only delete those files which haven't been used to certain time like some modified by date. I am working on a functionality where I have to store some data in the temp folder and then just push this data after processing to some remote location. I was thinking like what will happen if I am currently writing to some file in temp directory and in that particular time the clean-up is running and it delete that file as well

Answer 2

David Broggy 6,371 MVP Volunteer Moderator

Hi @HKPR
Yes, leaving data in a temp directory could definitely be a security issue.
If possible you should clean up temp once you’re done with it, or ensure you’re not sharing that directory outside of you function.
Good luck.

HKPR 41 Reputation points

2022-07-25T01:50:17.257+00:00
@David Broggy

Will the temp directory automatically clean up when my function is restarted?

temp directory D:\homeis self-contained so it is isolated to the processes within the sandbox - temp data is secure or not?
David Broggy 6,371 Reputation points MVP Volunteer Moderator

2022-07-25T13:08:34.547+00:00

Hi HPKR,
Personally, I would never assume something is secure, so I'd add a function to purge temp or to check if your files exist and then purge.
What the function does is subjective to the programmer that made it.
You can look at the contents of the function and see if it has a cleanup function.

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Temp directory files persistence in Azure Functions

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