Builders

Use cases will often involve more than simply copying files to the image. Many will require a build step: some process that creates additional files in the image's local filesystem needed at runtime.

Compiling an application from source

Given examples/hello-world-c as a working directory

And this "blubber.yaml"

version: v4
variants:
  build:
    base: debian:bullseye
    apt:
      packages:
        - gcc
        - libc6-dev
    builder:
      requirements: [main.c]
      command: "gcc -o hello main.c"
    entrypoint: [./hello]

When you build the "build" variant

Then the image will have the following files in the default working directory

hello

Compiling an application using multiple builders

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

And this "blubber.yaml"

version: v4
variants:
  build:
    base: golang:1.18
    builders:
      - custom:
          requirements: [go.mod, go.sum]
          command: "go mod download"
      - custom:
          requirements: [main.go]
          command: "go build ."
    entrypoint: [./hello-world-go]

When you build the "build" variant

Then the image will have the following files in the default working directory

hello-world-go

Defining inline builder scripts

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

And this "blubber.yaml"

version: v4
variants:
  build:
    base: golang:1.18
    runs:
      environment:
        CGO_ENABLED: "0"
    builders:
      - custom:
          requirements: [go.mod, go.sum]
          command: "go mod download"
      - custom:
          requirements: [main.go]
          script: |
            #!/bin/bash
            if ! [[ "$CGO_ENABLED" == "0" ]]; then
              echo "you must set CGO_ENABLED=0 for this build"
              exit 1
            fi
            go build $(go list)
  application:
    copies:
      - from: build
        source: ./hello-world-go
        destination: /hello
    entrypoint: [/hello]

When you build the "application" variant

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

hello

Excluding files from requirements by glob pattern

Given examples/hello-world-c as a working directory

And this "blubber.yaml"

version: v4
variants:
  build:
    base: debian:bullseye
    apt:
      packages:
        - gcc
        - libc6-dev
    builder:
      requirements:
        - from: local
          exclude: ["*.md"]
      command: "gcc -o hello main.c"
    entrypoint: [./hello]

When you build the "build" variant

Then the image will have the following files in the default working directory

hello

Then the image will not have the following files in the default working directory

README.md

Using caches to speed up builds

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

And this "blubber.yaml"

version: v4
variants:
  build:
    base: golang:1.18
    runs:
      environment:
        GOCACHE: /var/cache/go
    builders:
      - custom:
          requirements: [ go.mod, go.sum ]
          command: "go mod download"
          caches: [ "${GOPATH}/pkg" ]
      - custom:
          requirements: [main.go]
          command: "go build ."
          caches: [ "${GOCACHE}" ]
    entrypoint: [./hello-world-go]

When you build the "build" variant

Then the image will have the following files in the default working directory

hello-world-go

Using a mount to read files from another variant

Given examples/web-app as a working directory

And this "blubber.yaml"

version: v4
variants:
  assets:
    base: node:22-bookworm
    lives:
      in: /src
    builders:
      - node:
          requirements: [package.json, package-lock.json]
      - custom:
          requirements:
            - webpack.config.js
            - ./src/
          command: "npm run build"
  build:
    base: golang:1.23
    runs:
      environment:
        CGO_ENABLED: "0"
        GOCACHE: /var/cache/go
    builders:
      - custom:
          requirements: [go.mod, main.go]
          command: "go build"
          caches: [ "${GOCACHE}" ]
          mounts:
            - from: assets
              source: /src/dist
              destination: ./dist
  webserver:
    copies:
      - from: build
        source: ./web-app
        destination: /usr/bin/web-app
    entrypoint: [/usr/bin/web-app]

When you build the "webserver" variant

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

web-app

And the image entrypoint will be "/usr/bin/web-app".