Orion server crashes on windows because of event loop

[EmilRex]

First check

• I added a descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the Prefect documentation for this issue.
• I checked that this issue is related to Prefect and not one of its dependencies.

Bug summary

Running prefect orion start on a Windows machine results in an exception from Python's asyncio library related to the event loop. The underlying issue is documented in this StackOverflow post. The behavior is documented in this Community Slack post.

Reproduction

prefect orion start

Error

Versions

Additional context

No response

[zanieb]

@EmilRex please use text instead of screenshots, this content is not searchable now.

Is this definitely Python 3.9 and not 3.7? The default event loop changed in 3.8 to one that supports subprocesses. https://docs.python.org/3/library/asyncio-platforms.html#asyncio-windows-subprocess

[EmilRex]

@madkinsz Will do! Already requested the text from the user.

Is this definitely Python 3.9 and not 3.7?

I don't know for sure, but I can see that prefect version was run immediately before prefect orion start in the same terminal session, so I expect that it is:

[EmilRex]

^ This was after we asked the user to reproduce with v2.7.7

[peytonrunyan]

Additional context from the thread:

Hi @Emil Christensen.
I was able to get past and reproduce the issue. To get past the issue, I had to do the following. 1. Delete the file in C:\Users<user_name>\AppData\Roaming\Python. 2. Comment the code: @flow #(task_runner=DaskTaskRunner()). To reproduce the issue, all I have to do is uncomment the DaskTaskRunner. I agree its an issue running the DaskTaskRunner on Windows.

This issue appears to be a compatibility issue with the DaskTaskRunner on windows. I'll try to replicate in the morning.

cc'ing @ahuang11 since this is Dask related.

[zanieb]

Why is flow code involved at all if this error is supposed to be from running prefect orion start?

[EmilRex]

Why is flow code involved at all if this error is supposed to be from running prefect orion start?

I think it's a separate issue, but am not completely sure.

[zanieb]

I think this is related to general issues we're seeing with the event loop policy on Windows; see #8184

[zhen0]

Closing in favor of #8206