Magic Cache for GitHub Actions

RunsOn Magic Cache is a feature that allows you to transparently switch the GitHub Actions caching backend to use the local, fast, and unlimited S3 cache backend:

When the magic cache is enabled, the RunsOn agent will start a sidecar cache backend on the runner, and direct the various caching actions (including the gha cache backend for Docker Buildx) to send caching requests to the sidecar.

The sidecar will then transparently forward the requests to the S3 cache backend, and return the cache hits back to the caching actions.

This means that you can use the same caching configuration for your builds, regardless of whether you’re using the official GitHub Actions cache or the S3 cache.

Note that when running on official GitHub Actions runners, the runs-on/action@v1 action will just be a no-op, so it’s fine to keep in your workflows even if you mix official and RunsOn runners. This action will also soon be used to configure more advanced aspects of the runner, like CloudWatch monitoring, SSM agent enablement, etc.

As an example, the workflow below will compare the speed of the magic cache vs official runners for multiple cache sizes by generating a random file, saving it to the cache, and then restoring it from the cache. It uses the official actions/cache action to save and restore the cache, but it should also work with any language-specific caching actions (e.g. actions/setup-node, ruby/setup-ruby, etc.).

Leave a Comment