Caching build of Docker actions

Describe the enhancement

In my opinion, in the case of Docker actions, in many cases it is worthwhile to provide the cache for actions build. At least for published in the marketplace, it is possible to pre-build them by GitHub Actions and store as cache.

Currently, Docker actions are built multiple times as the first step of all builds, which is extremely inefficient for complex Docker actions.

Code Snippet This is due to the way the GitHub Actions worker works.

Additional information

The issue actions/toolkit#47 has been closed indicating a reference to @actions/cache, which however is limited to user data cache only. In this case, we do not have user data, but public actions, and the process is not controlled by the user at this stage (yet).

[peaceiris]

Now, we can pull a docker image from the Docker Hub or the GitHub Package Registry to skip a build step. But it is better the actions runner can cache a docker image with a built-in cache feature, not this cache action.

We are discussing at #37 that is focusing the Docker CLI, not a Docker action. We want to run a docker action with uses: key and cache it like the actions beta v1.

We can skip a docker action build step like the following as a current workaround:

- uses: peaceiris/actions-gh-pages@v2
+ uses: docker://peaceiris/gh-pages:v2

(Edit: Now, this action migrated to a TypeScript Action) GitHub Actions for GitHub Pages

Although, we cannot verify those images are trusted. I hope that we can build a docker action and cache it on the GitHub Actions runner.

[dungahk]

I’ve tried using the docker save/load strategy but it does not work when the Dockerfile has a COPY/ADD command because the SHA produced is always different, I’m not sure why that happens, I’ve tried both with Github managed runners and self-hosted. Self-hosted works if I don’t run docker system prune which makes sense I think.