Building Docker Images Efficiently with Pre-cached Dependencies

When constructing Docker images, it's crucial to minimize build time. One strategy is to cache dependencies. However, this requires building the dependencies first, which can be time-consuming.

Is there a way to pre-build multiple dependencies listed in the go.mod file?

The answer lies in utilizing Docker's caching mechanisms. The suggested Dockerfile structure includes a crucial caching layer:

FROM scratch
COPY --from=build /out/example /

This step copies the built executable from an intermediate build stage into the final image. However, the key ingredient is in the build stage:

RUN --mount=type=cache,target=/root/.cache/go-build go build -o /out/example .

This command mounts the default go build cache directory (/root/.cache/go-build) and executes the go build command. The cache ensures that dependencies are downloaded and compiled only once, significantly reducing build times for subsequent builds.

To enable caching, it's essential to set the DOCKER_BUILDKIT environment variable to 1:

DOCKER_BUILDKIT=1 docker build -t myimage .

By following these steps, you can pre-build all dependencies in go.mod and leverage caching to streamline your Docker image builds.