pwsh (PowerShellV2) tries to spawn powershell.exe process inside container with PowerShell Core

Type: Bug Task Name: pwsh (PowerShellV2)

Environment

Server

Azure DevOps Server Version 17.143.28912.1

Agent

Type: Private OS: Windows Server 1809 with Docker Version: vsts-agent-win-x64-2.144.2

Issue Description

I run pwsh task inside a mcr.microsoft.com/powershell:6.2.3-nanoserver-1809 container and get failure mentioning that node.js cannot spawn C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe process. I wonder why pwsh task needs to run powershell.exe process?

YAML definition excerpt

container:
  image: mcr.microsoft.com/powershell:6.2.3-nanoserver-1809

steps:
- pwsh: |
    # Inline script

Task logs

2019-09-27T11:17:12.7725567Z ==============================================================================
2019-09-27T11:17:12.7725614Z Task         : PowerShell
2019-09-27T11:17:12.7725642Z Description  : Run a PowerShell script on Windows, macOS, or Linux.
2019-09-27T11:17:12.7725676Z Version      : 2.140.2
2019-09-27T11:17:12.7725702Z Author       : Microsoft Corporation
2019-09-27T11:17:12.7725730Z Help         : [More Information](https://go.microsoft.com/fwlink/?LinkID=613736)
2019-09-27T11:17:12.7725767Z ==============================================================================
/* ... */
2019-09-27T11:17:13.0712078Z events.js:160
2019-09-27T11:17:13.0712509Z       throw er; // Unhandled 'error' event
2019-09-27T11:17:13.0712639Z       ^
2019-09-27T11:17:13.0714281Z 
2019-09-27T11:17:13.0720062Z Error: spawn C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe ENOENT
2019-09-27T11:17:13.0723425Z     at exports._errnoException (util.js:1018:11)
2019-09-27T11:17:13.0723712Z     at Process.ChildProcess._handle.onexit (internal/child_process.js:193:32)
2019-09-27T11:17:13.0723870Z     at onErrorNT (internal/child_process.js:367:16)
2019-09-27T11:17:13.0723990Z     at _combinedTickCallback (internal/process/next_tick.js:80:11)
2019-09-27T11:17:13.0724113Z     at process._tickCallback (internal/process/next_tick.js:104:9)
2019-09-27T11:17:13.1880286Z ##[error]Exit code 1 returned from process: file name 'C:\Program Files\Docker\docker.EXE', arguments 'exec -i 75c31673282e4f2396b2b1c44e37e07a683a7ad0e248aacbc0eaaf084541377d C:\__a\externals\node\bin\node.exe C:\__w\_temp\containerHandlerInvoker.js'.

[jtpetty]

I actually have a PR to fix this in the agent itself. https://github.com/microsoft/azure-pipelines-agent/pull/2767

The problem is that our task model uses either a Node or PowerShell handler to run the task, not PowerShell Core. On Windows, we always prefer the PowerShell handler, but in this case, there is no PowerShell in the container, only PowerShell Core.

[damccorm]

So, to interpret, if we set agent.preferPowerShellOnContainers to false on a nanoserver container, it should now work for pwsh scripts?

The powershell task itself should work. I would expect the commandline task to fail, though, since it would run its Node Handler Linux version which looks for bash.