try multiplatform build on PR

[erikarasnick]

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[erikarasnick]

Without making changes to Dockerfile (only added platform argument to final build), the entire GHA workflow took 4 hr 21 min. Most of this time was spent building the container (specifically renv::restore()) for arm64 since the virtual environment here is amd64 (on my local computer it's opposite). Looking into solutions for compiling the first build then converting to the other platform. I've been using this resource: https://www.docker.com/blog/faster-multi-platform-builds-dockerfile-cross-compilation-guide/ but not sure if it is directly applicable yet.

Also, the way it is currently set up, we are building the container 3 times-- once to use for testing, one final build for amd64 and one final build for arm64. As far as I can tell, you can't call a built container when building for multi-platform unless you push it to some repository first (i.e., when I build locally, then run di, it is not there) so I have it building for one platform for testing, then building multi-platform to be pushed to ghcr. I think there are ways to cache the first (test) build to be used for the amd64 final build-- still looking into that.

[erikarasnick]

hmm.. cross-compilation may not be possible in our case. all examples I have seen are for apps built with go, alpine, or rust (??) I'm out of my league 😅

[erikarasnick]

original GHA multi-platform documentation from Cole https://docs.docker.com/build/ci/github-actions/examples/#multi-platform-images