With Docker Desktop on WSL 2, how to find and inspect the exact host folder of a bind mount?

My main question is: with docker compose on Docker Desktop with WSL 2, when using a bind mount where the host path is a relative path, where and what is the actual host path on the WSL distro used by the docker desktop backend?

Sections below help understanding the context, what I searched and understood, and detail my questions.

Actual source issue


I have a docker compose configuration and a container with an Angular application. The content of the project is located on the Windows file system, and the docker compose uses a bind mount with a relative path.

The container does get the initial content, but it seems to never be updated: no live reload, no updated content when (hard-)refreshing the browser page.

Note that this is with Docker Desktop on Windows, after switching from the Hyper-V backend to the WSL 2 one. With Hyper-V, everything worked as expected, it was just much slower (as they state in the documentation).

My investigations


I really searched a lot... and got quite mad since I took many paths and always got badly stuck.

• I tried to run a WSL shell inside docker-desktop-data which was running: it fails, returning immediately, and the process exit code is just the generic 1 for error. Btw, doing the same for docker-desktop does work.
• I tried to find the content using the Windows explorer in the network folder \\wsl$\docker-desktop-data. There I could finally see the persisted volumes, but couldn't find any folder that would correspond to the bind mount
• I couldn't find the information about what internal path the docker engine exposes to the container (which is what my question's title targets). I could see the WSL distro had mounted paths corresponding to the Windows file system drives, but it doesn't mean that this is what it uses (and in fact, there I could see my content updated, while, as I said, nothing was updated when refreshing the browser hence my hypothesis that the content is lying elsewhere)
• I discovered the existence of the ext4.vhdx files located under C:\Users\<username>\AppData\Local\Docker\wsl\{data,distro}. I tried to mount it, but as expected it refused since it was already mounted. However I couldn't find any info about where to see the mounted content. It might by this \\wsl$\docker-desktop[-data] thing, but no doc, nor any command (I tried PowerShell's Get-VHD which just told me it's "attached") could tell me how to get that info.

And probably a few other things which I don't even remember and that were probably already too far from the initial topic.

I also checked the official Docker documentation pages with no luck finding these details.

My next step would be to read the source code of the backends directly...

My expectations


The real, pragmatic outcome for me is to be able to have the container interact with the local Windows file system content, instead of what seems to be a copy, which I can't locate.

As a bonus, I would love to understand what paths are involved, and what mechanisms are used to bind all of that (e.g. with the working Hyper-V backend, I expect a Hyper-V specific mechanism to have been used to make it possible for the virtualized docker process to expose a Linux path to the container which eventually was just a sort of hard link / shared folder - conceptually speaking - to the Windows file system folder). So, in docker compose's configuration I see a host <=> container path mapping, but being on Windows there's really a windows host <=> linux host <=> container mapping and it's that windows host <=> linux host mapping which seems to behave differently between Hyper-V and WSL 2, with me being unable to locate the linux host path.

If all of that could be backed by links to documentations (preferably reference/official) it would make it PERFECT.

But, really, getting a solution to the first point would already be extremely helpful.

Continue reading...