$env:PSModulePath set incorrectly for second instance when PSWorkerInProcConcurrencyUpperBound > 1

[kwill-MSFT]

Repro steps

1. Create new Functions project
2. Add 2 TimerTrigger functions, both with "schedule": "*/1 * * * * *"
3. Add Start-Sleep -Seconds 5 into the code for both timer functions. This ensures they both try to execute simultaneously.
4. In local.settings.json, set "PSWorkerInProcConcurrencyUpperBound": "2"
5. Include the Az modules in requirements.psd1
6. Add code to profile.ps1 which imports an Az module. The following is what I used to narrow down the problem:

Write-Information "Running profile.ps1"
Write-Information "PSModulePath = $($env:PSModulePath)"
Get-Module Az.Resources -ListAvailable | fl Name, Path
Import-Module Az.Resources
Get-AzLocation | Out-Null
Write-Information "Done in profile.ps1"

Result:

For detailed output, run func with --verbose flag.
[2021-06-16T01:24:00.034Z] Executing 'Functions.TimerTrigger2' (Reason='Timer fired at 2021-06-15T20:24:00.0138898-05:00', Id=fc897759-bc62-4fb5-974c-cf0a5e882d20)
[2021-06-16T01:24:00.034Z] Executing 'Functions.TimerTrigger1' (Reason='Timer fired at 2021-06-15T20:24:00.0138896-05:00', Id=927dca38-8e2a-4bc4-9ed7-255174224d05)
[2021-06-16T01:24:00.698Z] Worker process started and initialized.
[2021-06-16T01:24:01.234Z] INFORMATION: Running profile.ps1
[2021-06-16T01:24:01.239Z] INFORMATION: PSModulePath = C:\Users\xxx\AppData\Local\AzureFunctions\FunctionsPSWorkerInProcConcurrencyUpperBoundIssue\ManagedDependencies\210616004428282.r;C:\Temp\Projects\FunctionsPSWorkerInProcConcurrencyUpperBoundIssue\Modules;C:\Users\xxx\AppData\Roaming\npm\node_modules\azure-functions-core-tools\bin\workers\powershell\7\Modules
[2021-06-16T01:24:01.360Z] OUTPUT: 
[2021-06-16T01:24:01.385Z] OUTPUT: Name : Az.Resources
[2021-06-16T01:24:01.388Z] OUTPUT: Path : C:\Users\xxx\AppData\Local\AzureFunctions\FunctionsPSWorkerInProcConcurrencyUpperBoundIssue\ManagedDependencies\210616004428282.r\Az.Resources\4.2.0\Az.Resources.psd1
[2021-06-16T01:24:01.389Z] OUTPUT: 
[2021-06-16T01:24:01.391Z] OUTPUT: 
[2021-06-16T01:24:04.746Z] Host lock lease acquired by instance ID '0000000000000000000000004BCB02C4'.
[2021-06-16T01:24:08.376Z] INFORMATION: Done in profile.ps1
[2021-06-16T01:24:08.473Z] INFORMATION: Running profile.ps1
[2021-06-16T01:24:08.477Z] INFORMATION: PSModulePath = C:\Users\xxx\Documents\PowerShell\Modules;C:\Program Files\PowerShell\Modules;c:\users\xxx\appdata\roaming\npm\node_modules\azure-functions-core-tools\bin\workers\powershell\7\runtimes\win\lib\netcoreapp3.1\Modules;C:\Users\xxx\AppData\Local\AzureFunctions\FunctionsPSWorkerInProcConcurrencyUpperBoundIssue\ManagedDependencies\210616004428282.r;C:\Temp\Projects\FunctionsPSWorkerInProcConcurrencyUpperBoundIssue\Modules;C:\Users\xxx\AppData\Roaming\npm\node_modules\azure-functions-core-tools\bin\workers\powershell\7\Modules
[2021-06-16T01:24:08.534Z] OUTPUT: 
[2021-06-16T01:24:08.537Z] OUTPUT: Name : Az.Resources
[2021-06-16T01:24:08.539Z] OUTPUT: Path : C:\Users\xxx\Documents\PowerShell\Modules\Az.Resources\3.4.1\Az.Resources.psd1
[2021-06-16T01:24:08.541Z] OUTPUT: 
[2021-06-16T01:24:08.542Z] OUTPUT: Name : Az.Resources
[2021-06-16T01:24:08.543Z] OUTPUT: Path : C:\Users\xxx\AppData\Local\AzureFunctions\FunctionsPSWorkerInProcConcurrencyUpperBoundIssue\ManagedDependencies\210616004428282.r\Az.Resources\4.2.0\Az.Resources.psd1
[2021-06-16T01:24:08.545Z] OUTPUT: 
[2021-06-16T01:24:08.547Z] OUTPUT: 
[2021-06-16T01:24:08.872Z] ERROR: Assembly with same name is already loaded
[2021-06-16T01:24:08.874Z] 
[2021-06-16T01:24:08.875Z] Exception             : 
[2021-06-16T01:24:08.877Z]     Type       : System.IO.FileLoadException
[2021-06-16T01:24:08.879Z]     Message    : Assembly with same name is already loaded

The first time profile.ps1 executes, PSModulePath is correct and only shows a single Az.Resources module available.

The second time profile.ps1 executes, PSModulePath includes 'C:\Users\xxx\Documents\PowerShell\Modules' and results in 2 available Az.Resources modules available. This then results in the FileLoadException.

This can be worked around by manually setting the $env:PSModulePath in profile.ps1 prior to the Import-Module line.

[AnatoliB]

Thank you @kwill-MSFT.

A few more details:

• Something somewhere adds C:\Users\xxx\Documents\PowerShell\Modules and C:\Program Files\PowerShell\Modules folders to the process-scoped PSModulePath environment variable. These folders are usually automatically added by the stand-alone pwsh.exe, but we don't use the stand-alone pwsh.exe in the worker, and the worker sets its own PSModulePath value explicitly (the first value in the the traces is the correct one). Apparently, the code path we hit when the second runspace is created modifies PSModulePath again. But I don't see that in the worker code, so this must be happening in the PowerShell SDK. We need to find a way to suppress this.
• This should be affecting local runs only, not apps deployed to the cloud, as there is no modules installed to these locations anyway.

Workarounds:

• The most reliable workaround is removing the conflicting module versions from these two folders on the local machine. Consider running Functions host in a container, to have a clean and controlled environment.
• Modifying PSModulePath in profile.ps1 may work as well, but this is less reliable because the variable is process-scoped, and modules may be imported by multiple concurrent function invocations any time, so having PSModulePath set incorrectly even for a short time interval creates an opportunity for something to break again.