One of Docker’s goals has always been to provide the best experience working with containers from a Desktop environment, with an experience as close to native as possible whether you are working on Windows, Mac or Linux. We spend a lot of time working with the software stacks provided by Microsoft and Apple to achieve this. As part of this work, we have been closely monitoring Windows Subsystem for Linux (WSL) since it was introduced in 2016, to see how we could leverage it for our products.
The original WSL was an impressive effort to emulate a Linux Kernel on top of Windows, but there are such foundational differences between Windows and Linux that some things were impossible to implement with the same behavior as on native Linux, and this meant that it was impossible to run the Docker Engine and Kubernetes directly inside WSL. Instead, Docker Desktop developed an alternative solution using Hyper-V VMs and LinuxKit to achieve the seamless integration our users expect and love today.
Microsoft has just announced WSL 2 with a major architecture change: instead of using emulation, they are actually providing a real Linux Kernel running inside a lightweight VM. This approach is architecturally very close to what we do with LinuxKit and Hyper-V today, with the additional benefit that it is more lightweight and more tightly integrated with Windows than Docker can provide alone. The Docker daemon runs well on it with great performance, and the time it takes from a cold boot to have dockerd running in WSL 2 is around 2 seconds on our developer machines. We are very excited about this technology, and we are happy to announce that we are working on a new version of Docker Desktop leveraging WSL 2, with a public preview in July. It will make the Docker experience for developing with containers even greater, unlock new capabilities, and because WSL 2 works on Windows 10 Home edition, so will Docker Desktop.
Collaborating with Microsoft
As part of our shared effort to make Docker Desktop the best way to use Docker on Windows, Microsoft gave us early builds of WSL 2 so that we could evaluate the technology, see how it fits with our product, and share feedback about what is missing or broken. We started prototyping different approaches and we are now ready to share a little bit about what is coming in the next few months.
Docker Desktop Future
We will replace the Hyper-V VM we currently use by a WSL 2 integration package. This package will provide the same features as the current Docker Desktop VM: Kubernetes 1-click setup, automatic updates, transparent HTTP proxy configuration, access to the daemon from Windows, transparent bind mounts of Windows files, and more.
This integration package will contain both the server side components required to run Docker and Kubernetes, as well as the CLI tools used to interact with those components within WSL. We will then be able to introduce a new feature with Docker Desktop: Linux workspaces.
When using Docker Desktop today, the VM running the daemon is completely opaque: you can interact with the Docker and Kubernetes API from Windows, but you can’t run anything within the VM except Docker containers or Kubernetes Pods.
With WSL 2 integration, you will still experience the same seamless integration with Windows, but Linux programs running inside WSL will also be able to do the same. This has a huge impact for developers working on projects targeting a Linux environment, or with a build process tailored for Linux. No need for maintaining both Linux and Windows build scripts anymore! As an example, a developer at Docker can now work on the Linux Docker daemon on Windows, using the same set of tools and scripts as a developer on a Linux machine:
Also, bind mounts from WSL will support inotify events and have nearly identical I/O performance as on a native Linux machine, which will solve one of the major Docker Desktop pain points with I/O-heavy toolchains. NodeJS, PHP and other web development tools will benefit greatly from this feature.
Combined with Visual Studio Code “Remote to WSL”, Docker Desktop Linux workspaces will make it possible to run a full Linux toolchain for building containers on your local machine, from your IDE running on Windows.
With WSL 2, Microsoft put a huge amount of effort into performance and resource allocations: The VM is setup to use dynamic memory allocation, and can schedule work on all the Host CPUs, while consuming as little (or as much) memory it requires – within the limits of what the host can provide, and in a collaborative manner towards win32 processes running on the host.
Docker Desktop will leverage this to greatly improve its resource consumption. It will use as little or as much CPU and memory as it needs, and CPU/Memory intensive tasks such as building a container will run much faster than today.
In addition, the time to start a WSL 2 distribution and the Docker daemon after a cold start is blazingly fast – within 2s on our development laptops, compared to tens of seconds in the current version of Docker Desktop. This opens the door to battery-life optimizations by deferring the daemon startup to the first API call, and automatically stop the daemon when it is not running any container.
Zero-configuration bind mount support
One of the major issues users have today with Docker Desktop – especially in an enterprise environment – is the reliability of Windows file bind mounts. The current implementation relies on Samba Windows service, which may be deactivated, blocked by enterprise GPOs, blocked by 3rd party firewalls etc. Docker Desktop with WSL 2 will solve this whole category of issues by leveraging WSL features for implementing bind mounts of Windows files. It will provide an “it just works” experience, out of the box.
Technical Preview of Docker Desktop for WSL 2
Thanks to our collaboration with Microsoft, we are already hard at work on implementing our vision. We have written core functionalities to deploy an integration package, run the daemon and expose it to Windows processes, with support for bind mounts and port forwarding.
A technical preview of Docker Desktop for WSL 2 will be available for download in July. It will run side by side with the current version of Docker Desktop, so you can continue to work safely on your existing projects. If you are running the latest Windows Insider build, you will be able to experience this first hand. In the coming months, we will add more features until the WSL 2 architecture is used in Docker Desktop for everyone running a compatible version of Windows.