The codebase itself is built on Node JS, but I have to run it in WSL.  There are various build issues that keep it from building cleanly in Windows and it would be a bit of work to fix that.  But it builds just fine under WSL, so it's easier to use that.

The dev setup uses a Docker container running HAProxy.  It's set up to proxy the static portion of the website to the shared dev server (which is on the VPN) and direct the traffic for the dynamic part to a local port.  So we have a HAProxy running in Docker, the local dev server running in WSL, and the browser running in Windows.

The problem: In the default WSL config, this doesn't work.  The proxy to the shared server works just fine.  So if I go to wwwlocal.site.com, that works as a proxy to wwwdev.site.com.  Perfect!  However, wwwlocal.site.com/login is supposed to proxy to localhost:4321, but that results in a 503 error.  However, I can go directly to localhost:4321 and it works just fine, so this is clearly a networking issue.

The solution was to just add a few lines to my $home\.wslconfig file on Windows.  The following lines did the trick:

[wsl2]
networkingMode=mirrored
dnsTunneling=true
autoProxy=true

You can read more about these settings here.