Copying from other variants

Build dependencies can add up quickly, and in most cases you don't want them around in your production image if they're not needed at runtime. You can copy files from a build variant into a more minimal production variant in a couple of different ways.

Background

Given examples/hello-world-go as a working directory.

Copying from another variant using "copies.from"

Given this "blubber.yaml"

version: v4
variants:
  build:
    base: golang:1.18
    lives:
      in: /src
    builders:
      - custom:
          requirements: [go.mod, go.sum]
          command: "go mod download"
      - custom:
          requirements: [main.go]
          command: "go build ."
  production:
    base: ~ # Go binaries are statically linked, so we can even use a scratch image here
    copies:
      - from: build
        source: /src/hello-world-go
        destination: /hello-world
    entrypoint: [/hello-world]

When you build the "production" variant

Then the image will have the following files in "/"

hello-world