Question: How is docker run cache handled across rebuilds

[nmiculinic]

For example I have the following lines in the dockerfile:

RUN --mount=type=cache,target=/go/pkg/mod go mod download
RUN --mount=type=cache,target=/root/.cache/go-build --mount=type=cache,target=/go/pkg/mod CGO_ENABLED=0 go build -ldflags "${LDFLAGS}" -o app ./cmd/controlplane

How are those cache lines handled across rebuilds? I'm missing details in the documentation to understand what's happening.

[crazy-max]

@nmiculinic

How are those cache lines handled across rebuilds?

This type of cache is internal and as the GitHub Runners are ephemeral the BuildKit state volume is lost. But if you have a self-hosted runner it should be reused if you stick to the same builder.

I guess we could handle a specific cache for this volume in the GitHub Action itself with @actions/cache. cc @tonistiigi

[Richard87]

This would be amazing for my RUN yarn install and RUN composer install lines!

[crazy-max]

Since docker/buildx#672 BuildKit state is saved in a named volume. We should be able to cache it and mount it back but that would require some changes in the setup-buildx-action. Will think about it.

[crazy-max]

Tracked in docker/setup-buildx-action#122