10x faster arm64 builds on Github Actions

@SuperSeriousBot is my playground. When I experiment with anything new, I use it as a testbed of sorts. It has served me well (over 4 years!) and is in a state of constant flux.

The latest addition to the Frankenstein’s monster that is @SuperSeriousBot, is arm64 builds of the base Docker image.

However…

These build times are despite extremely aggressive artifact caching (almost 1.2GB in size now). Since Github (as of 2022) offers only x86 runners for Actions, the arm64 images need to be built via QEMU emulation, leading to these long waits. Something needed to be done. I pushed a change to the repo and got down to work.

Appending Buildx Nodes

I’ve already been using buildx for all my Docker needs. I found this gem of an action called baschny/append-buildx-action which will append a buildx node to an already setup action.

It does this by SSH-ing into a self-hosted runner and running the docker buildx create command. All it needs is the IP address of the self-hosted runner and the private key to SSH into it.

It was so painless that all I needed to do was provide the machine and add the following lines to my workflow:

- name: "Append ARM buildx builder"
  uses: baschny/append-buildx-action@v1
  with:
    builder: ${{ steps.builder.outputs.name }}
    endpoint: "ssh://ubuntu@${{ secrets.SSH_HOST }}"
    ssh_private_key: ${{ secrets.ARM64_RUNNER_SSH_PRIVATE_KEY }}

I was able to get this working before the last change had even finished building!

Results

Very nearly a 10x improvement.

À bientôt!