Docker Desktop: WSL 2 Best practices

Docker Desktop WSL 2 backend has now been available for a few months for Windows 10 insider users and Microsoft just released WSL 2 on the Release Preview channel (which means GA is very close). We and our early users have accumulated some experience working with it and are excited to share a few best practices to implement in your Linux container projects!

Docker Desktop with the WSL 2 backend can be used as before from a Windows terminal. We focused on compatibility to keep you happy with your current development workflow.

But to get the most out of Windows 10 2004 we have some recommendations for you.

Fully embrace WSL 2

The first and most important best practice we want to share, is to fully embrace WSL 2. Your project files should be stored within your WSL 2 distro of choice, you should run the docker CLI from this distro, and you should avoid accessing files stored on the Windows host as much as possible.

For backward compatibility reasons, we kept the possibility to interact with Docker from the Windows CLI, but it is not the preferred option anymore.

Running docker CLI from WSL will bring you…

Awesome mounts performance

Both your own WSL 2 distro and docker-desktop run on the same utility VM. They share the same Kernel, VFS cache etc. They just run in separate namespaces so that they have the illusion of running totally independently. Docker Desktop leverages that to handle bind mounts from a WSL 2 distro without involving any remote file sharing system. This means that when you mount your project files in a container (with docker run -v ~/my-project:/sources <...>), docker will propagate inotify events and share the same cache as your own distro to avoid reading file content from disk repeatedly.

A little warning though: if you mount files that live in the Windows file system (such as with docker run -v /mnt/c/Users/Simon/windows-project:/sources <...>), you won’t get those performance benefits, as /mnt/c is actually a mountpoint exposing Windows files through a Plan9 file share. 

Compatibility with Linux toolchains and build scripts

Most reasonably sized projects involving Linux containers come with a bunch of automation scripts. Those scripts are often developed for Linux first (because most of the time, CI/CD pipelines for those projects run on Linux), and developers running on Windows are often considered second-class citizens. They are often using less polished versions of those scripts, and have to deal with subtle behavioral differences.

By fully embracing WSL 2, Windows developers can use the exact same build and automation scripts as on Linux. This means that Windows-specific scripts don’t need to be maintained anymore. Also, that means that you won’t experience issues with different line endings between Windows and Mac/Linux users!

What about my IDE?

If you want an IDE for editing your files, you can do that even if they are hosted within your WSL 2 distro. There are 3 different ways:

• Use Visual Studio Code Remote to WSL extension

If your IDE is Visual Studio Code, using Remote to WSL is the best way to continue working on your project. Visual Studio Code architecture is based on a client/server approach where pretty much everything except rendering and input processing is done in a server process, while the UI itself runs in a client process. Remote to WSL leverages that to run the whole server process within WSL while the UI runs as a classic win32 process.

That means that you get the same experience as before, but all your language services, terminals etc. run within WSL.

For more information, see Microsoft’s VS Code Remote to WSL documentation.

• Point your IDE to your distro network share

WSL provides a network share for each of your running distros. For example, if I have a project in my Ubuntu distro at `~/wall-e`, I can access it from Windows Explorer (and from any Windows Process) via the special network share `\\wsl$\Ubuntu\home\simon\wall-e`. 

• Run an X11 server on Windows, and run a Linux native IDE

The setup is a bit more complicated, but you always have the possibility to run an X11 server on Windows (VcXsrv, X410,…) and configure your DISPLAY environment variable such that GUI apps on Linux get rendered properly.

Use BuildKit and multi-stage builds

Docker Desktop WSL 2 backend has access to all your CPU cores. To leverage this as much as possible (and also to get access to the latest build features), you should enable BuildKit by default.

The easiest way to do that is to add the following line to your ~/.profile file:

export DOCKER_BUILDKIT=1.

This way, anytime you run docker build, it will run the build with the awesome BuildKit which is capable of running different build stages concurrently.

Use resource limits

Docker Desktop WSL 2 backend can use pretty much all CPU and memory resources on your machine. This is awesome for most cases, but there is a category of workloads where this can cause issues. Indeed, some containers (mainly databases, or caching services) tend to allocate as much memory as they can, and leave other processes (Linux or Win32) starving. Docker provides a way to impose limits in allocatable memory (as well as quotas on CPU usage) by a container. You can find documentation about it here: https://docs.docker.com/config/containers/resource_constraints/.

Reclaim cached memory

WSL 2 automatically reclaims memory when it is freed, to make it available to Windows processes. However, if the kernel decides to keep content in cache (and with Docker, it tends to happen quite a lot), the amount of memory reclaimed might not be sufficient.

To reclaim more memory, after stopping your containers, you can run echo 1 > /proc/sys/vm/drop_caches as root to drop the kernel page cache and make WSL 2 reclaim memory used by its VM.

What next

We are excited for people to use Docker Desktop with WSL 2 and hope that the tips and tricks in this article will help you get the best performance for all of your workloads. 

If you have another tip or idea you want to share with us for using Docker send us a tweet @docker or if you have feedback on our implementation then raise a ticket against our Github Repo.