This post was most recently updated on September 19th, 2021.

2 min read.

Well, that title is a mouthful. But it’s the topic for today, so what can you do?

That said, this article should be pretty topical, as the issue started popping up only a few days ago. Chances are it’ll be patched soon enough, but in the meantime, it’s always useful to document the fix!

Problem

Table of Contents

When running or debugging Azure Functions locally, your runtime just blurts our this error and fails to compile your functions:

[2021-01-11T10:28:11.495Z] A host error has occurred during startup operation '0d00defa-b8bd-4fb8-9794-b0e5950a4c38'.
[2021-01-11T10:28:11.499Z] System.IO.FileSystem: Could not find a part of the path 'C:\Users\username\AppData\Local\AzureFunctionsTools\Releases\3.17.0\workers'.
Value cannot be null. (Parameter 'provider')
Press any to continue….[2021-01-11T10:28:12.625Z] A host error has occurred during startup operation 'beca4180-a97c-4fab-b3d8-2323dbf5512d'.
[2021-01-11T10:28:12.628Z] System.IO.FileSystem: Could not find a part of the path 'C:\Users\username\AppData\Local\AzureFunctionsTools\Releases\3.17.0\workers'.
[2021-01-11T10:28:14.762Z] A host error has occurred during startup operation '447864ad-026f-462d-9d8d-70f95703baa8'.
[2021-01-11T10:28:14.764Z] System.IO.FileSystem: Could not find a part of the path 'C:\Users\username\AppData\Local\AzureFunctionsTools\Releases\3.17.0\workers'.

And this is what it actually looks like:

"System.IO.FileSystem: Could not find a part of the path \AppData\Local\AzureFunctionsTools\Releases\3.17.0\workers. Value cannot be null. (Parameter 'provider')" getting thrown when running Azure Functions locally. — “System.IO.FileSystem: Could not find a part of the path \AppData\Local\AzureFunctionsTools\Releases\3.17.0\workers. Value cannot be null. (Parameter ‘provider’)” getting thrown when running Azure Functions locally.

What do?

Solution

This one turned out to be easy to fix. Let me show the steps below!

Time needed: 5 minutes

How to fix “System.IO.FileSystem: Could not find a part of the path \AppData\Local\AzureFunctionsTools\Releases\3.17.0\workers. Value cannot be null. (Parameter ‘provider’)” when running Azure Functions locally?

Copy-paste the path the CLI is complaining about
That’s going to be something along the lines of:
‘C:\Users\your username here\AppData\Local\AzureFunctionsTools\Releases\3.17.0\workers
Remove the last part (workers) and open the directory in File Explorer
The screenshot below shows what you should see – the “workers” folder really does not exist.
Create a new folder called “workers”
It doesn’t matter if it’s empty. No need to copy anything over from previous AzureFunctionsTools (although you can if you really want to). You just need a new empty folder named “workers”.

Like in the screenshot below:

Run your functions again
It should now work – like magic :)

And there we go – you should be good (for now).

Did it work for you? Let me know in the comments -section below!

References

“Azure Functions local debugging broke with 3.17.0 update” 🙃
- https://developercommunity.visualstudio.com/content/problem/1304718/azure-functions-local-debugging-broke-with-3170-up.html

Author
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Antti K. Koskela

Developer / Speaker / Consultant at Koskila / Precio Fishbone / Norppandalotti Software Co / Alter - Experience Ideas Ltd

Antti Koskela is a proud digital native nomadic millennial full stack developer (is that enough funny buzzwords? That's definitely enough funny buzzwords!), who works as Solutions Architect for Precio Fishbone, building delightful Digital Workplaces.

He's been a developer from 2004 (starting with PHP and Java), and he's been working on .NET projects, Azure, Office 365, SharePoint and a lot of other stuff. He's also Microsoft MVP for Azure.

This is his personal professional (e.g. professional, but definitely personal) blog.

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