I’ve been spending a bit of time trying out Docker over the past few days, with the goal of making builds more reliable and repeatable.

Docker Desktop for Windows has the ability to run in Windows mode and Linux mode. Usually that means you can only run containers of one OS at at a time.

However, if you run configure Docker to enable ‘Experimental’ mode, then you can actually run both platforms simultaneously.

Interestingly, when you’re in this mode and you set ‘Windows’ as the default container platform, you don’t see an extra virtual machine listed in HyperV.

Here’s Docker running with Linux containers: Hyper-V Manager showing Docker virtual machine

And here’s Docker with Windows containers: Hyper-V Manager showing Docker machine not running Notice the VM may be there, but it is not running, even when I’m actually building a Linux container when that screenshot was taken.

So with experimental mode on, how can Docker be also running Linux containers in Windows mode?

Currently it uses something called LCOW - Linux Containers on Windows.

I know Docker also has preview support for WSL2. I think the plan is that once that ships (presumably with Windows 10 20H1) then Docker will be able to leverage that for Linux execution.

So in theory, if you need to spin up Linux and Windows containers, then this is the technology that will make that happen.

There’s still a few rough edges - probably why it’s all behind ‘preview’ or ‘experimental’ flags.

I hit one issue where trying to spin up a Node Linux container which has a step to run yarn resulted in some weird internal error:

Step 14/22 : RUN yarn
---> Running in eb14f055a9aa
container eb14f055a9aaa23db5f35493feec9009b775c6688e3c488b26c6880517bdd9f1 encountered an error during CreateProcess: failure in a Windows system call: Unspecified error (0x80004005)
[Event Detail: failed to run runc create/exec call for container eb14f055a9aaa23db5f35493feec9009b775c6688e3c488b26c6880517bdd9f1: exit status 1 Stack Trace:

No idea what’s going on there other than maybe I’ve managed to hit some issue where some API isn’t implemented?

It’s strange, as a different container (based on a different Linux distribution) didn’t have that problem.

So it has potential, but it’s obviously a work in progress.