Coding, How to, kubernetes

How to build Kubernetes from source and test in Kind with VSCode & devcontainers

I found myself last week looking at a bit of code in K8s which I thought I could make better, so I set about trying to understand how to clone, change and test it.

Luckily K8s has some good docs, trust these over me as they’re a great guide. This blog is more of a brain dump of how I got on trying with Devcontainers and VSCode. This is my first try at this so I’ve likely got lots of things wrong.

Roughly I knew what I needed as I’d heard about:

  1. Bazel for the Kubernetes build
  2. Kind to run a cluster locally
  3. Kubetest for running end2end tests

As the K8s build and testing cycle can use up quite a bit of machine power I didn’t want be doing all this on my laptop and ideally I wanted to capture all the setup in a nice repeatable way.

Enter DevContainers for VSCode, I’ve got them setup on my laptop to actually run on a meaty server for me and I can use them to capture all the setup requirements for building K8s.

After a lot of wrangling I got a Dockerfile and devcontainer.json file together which mount and install the required bits (warning: There may be lots wrong with this, I’m pretty new to the world of building K8s from source).

Now all I need to do is clone K8s, drop these two files into a .devcontainer folder and open the folder in VSCode. Once open you get prompted to open the folder in the devcontainer and away you go.

What do you do now?

  • Make the change you want to make
  • Build an image for kind with your changes:
kind build node-image --type bazel \
 -v 5 --image kindest/node:lawrence
  • Start a cluster based off that image:
kind create cluster --name lg \
--image kindest/node:lawrence
  • You can run the e2e tests too (still getting to grips with this)
kubetest --up --test --down \
--deployment=kind \
--kind-node-image=kindest/node:lawrence \
--provider=skeleton

The best part? All of this runs nicely in VSCode like its running locally but behind the scenes it’s on a remote server. The left window is my laptop and the right is the server doing a build.

Let me try it

Here is a Gist of my devcontainer files for you to play with. If you spot something silly I’m doing please let me know!

Current devcontainer setup (WIP)
Standard

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