Over the last year, I’ve gone from Linux n00b to a growing level of competence. In large part, this is thanks to Windows Subsystem for Linux, where I could learn and take advantage of command line tooling without being completely lost in an unfamiliar ecosystem. It also gave me an easy way to exit vim!

That said, I’m always interested to push the limits on things. After Brian Ketelsen’s recent post about WSL metadata, and some good conversation on Twitter, I was reminded that I had cross-compiled Kubernetes for Windows under WSL a while back, and had never shared how to repeat this feat of nerdery for others.

Setting up WSL 🔗

First up, you’ll need the Go programming language. I’ve got mine installed in the default location at /usr/local/go. I’m also using a common path for both Linux and Windows, so I’ve got my GOPATH environment variable pointed to the C: drive

# Optional: use a common directory for Windows & Linux
export GOPATH=/mnt/c/code/go

curl -LO https://dl.google.com/go/go1.9.3.linux-amd64.tar.gz
tar -C /usr/local -xzf go1.9.3.linux-amd64.tar.gz

Note: Kubernetes supports specific versions of Go. If you’ve already upgraded to 1.10, downloading a supported version and making sure it’s the active one in your PATH temporarily works great too!

You can check your version with go version and which executable is active with which go

Windows Defender 🔗

A quick note on Windows Defender before I continue - WSL is still working to catch up to native Linux installs on file I/O speed, but the built-in antivirus doesn’t make matters any better. I’ve made the decision to accept the risk and exclude my WSL and code folders from scanning, which seems to help. YMMV

Getting Kubernetes 🔗

Getting started with Kubernetes is easy! I followed the first part of the instructions on the main Kubernetes repository on GitHub.

go get -d k8s.io/kubernetes
cd $GOPATH/src/k8s.io/kubernetes

For me, that pulls everything down into /mnt/c/code/go/src/k8s.io/kubernetes, which is really mapped to C:\code\go\k8s.io\kubernetes. Neat!

Building Kubernetes 🔗

Even though I first did this back in November, I’m just getting started building & working with the Kubernetes codebase - especially on Windows. So don’t look to the snippet below as authoritative or best instructions, but they work for me!

# Build for Linux first to generate some needed files
make WHAT=cmd/kubelet KUBE_BUILD_PLATFORMS=linux/amd64

# Build kubelet and kube-proxy!
make WHAT=cmd/kubelet KUBE_BUILD_PLATFORMS=windows/amd64
make WHAT=cmd/kube-proxy KUBE_BUILD_PLATFORMS=windows/amd64

The commands will drop a kubelet.exe and a kube-proxy.exe in C:\code\go\src\k8s.io\kubernetes\_output\local\bin\windows\amd64. I’m ready to take these files, and run them locally, or upload them to a VM to do some real-world testing.

Summary 🔗

Awesome! I’ve just used a Linux installation of Go, running under Windows Subsystem for Linux, to compile a big-time real-world app for another operating system. Sure, it might not be the Kubernetes community’s first choice for toolchain, but it shows that WSL is a legit tool, and not just for toy apps or neat demos. WSL can and does support real engineering work, and things are only getting better and better. Keep an eye on the WSL team blog for more updates!