docs/content/manuals/build/bake/inheritance.md

title	linkTitle	weight	description	keywords
Inheritance in Bake	Inheritance	30	Learn how to inherit attributes from other targets in Bake	buildx, buildkit, bake, inheritance, targets, attributes

Targets can inherit attributes from other targets, using the inherits attribute. For example, imagine that you have a target that builds a Docker image for a development environment:

target "app-dev" {
  args = {
    GO_VERSION = "{{% param example_go_version %}}"
  }
  tags = ["docker.io/username/myapp:dev"]
  labels = {
    "org.opencontainers.image.source" = "https://github.com/username/myapp"
    "org.opencontainers.image.author" = "moby.whale@example.com"
  }
}

You can create a new target that uses the same build configuration, but with slightly different attributes for a production build. In this example, the app-release target inherits the app-dev target, but overrides the tags attribute and adds a new platforms attribute:

target "app-release" {
  inherits = ["app-dev"]
  tags = ["docker.io/username/myapp:latest"]
  platforms = ["linux/amd64", "linux/arm64"]
}

Common reusable targets

One common inheritance pattern is to define a common target that contains shared attributes for all or many of the build targets in the project. For example, the following _common target defines a common set of build arguments:

target "_common" {
  args = {
    GO_VERSION = "{{% param example_go_version %}}"
    BUILDKIT_CONTEXT_KEEP_GIT_DIR = 1
  }
}

You can then inherit the _common target in other targets to apply the shared attributes:

target "lint" {
  inherits = ["_common"]
  dockerfile = "./dockerfiles/lint.Dockerfile"
  output = [{ type = "cacheonly" }]
}

target "docs" {
  inherits = ["_common"]
  dockerfile = "./dockerfiles/docs.Dockerfile"
  output = ["./docs/reference"]
}

target "test" {
  inherits = ["_common"]
  target = "test-output"
  output = ["./test"]
}

target "binaries" {
  inherits = ["_common"]
  target = "binaries"
  output = ["./build"]
  platforms = ["local"]
}

Overriding inherited attributes

When a target inherits another target, it can override any of the inherited attributes. For example, the following target overrides the args attribute from the inherited target:

target "app-dev" {
  inherits = ["_common"]
  args = {
    GO_VERSION = "1.17"
  }
  tags = ["docker.io/username/myapp:dev"]
}

The GO_VERSION argument in app-release is set to 1.17, overriding the GO_VERSION argument from the app-dev target.

For more information about overriding attributes, see the Overriding configurations page.

Inherit from multiple targets

The inherits attribute is a list, meaning you can reuse attributes from multiple other targets. In the following example, the app-release target reuses attributes from both the app-dev and _common targets.

target "_common" {
  args = {
    GO_VERSION = "{{% param example_go_version %}}"
    BUILDKIT_CONTEXT_KEEP_GIT_DIR = 1
  }
}

target "app-dev" {
  inherits = ["_common"]
  args = {
    BUILDKIT_CONTEXT_KEEP_GIT_DIR = 0
  }
  tags = ["docker.io/username/myapp:dev"]
  labels = {
    "org.opencontainers.image.source" = "https://github.com/username/myapp"
    "org.opencontainers.image.author" = "moby.whale@example.com"
  }
}

target "app-release" {
  inherits = ["app-dev", "_common"]
  tags = ["docker.io/username/myapp:latest"]
  platforms = ["linux/amd64", "linux/arm64"]
}

When inheriting attributes from multiple targets and there's a conflict, the target that appears last in the inherits list takes precedence. The previous example defines the BUILDKIT_CONTEXT_KEEP_GIT_DIR in the _common target and overrides it in the app-dev target.

The app-release target inherits both app-dev target and the _common target. The BUILDKIT_CONTEXT_KEEP_GIT_DIR argument is set to 0 in the app-dev target and 1 in the _common target. The BUILDKIT_CONTEXT_KEEP_GIT_DIR argument in the app-release target is set to 1, not 0, because the _common target appears last in the inherits list.

Reusing single attributes from targets

If you only want to inherit a single attribute from a target, you can reference an attribute from another target using dot notation. For example, in the following Bake file, the bar target reuses the tags attribute from the foo target:

target "foo" {
  dockerfile = "foo.Dockerfile"
  tags       = ["myapp:latest"]
}
target "bar" {
  dockerfile = "bar.Dockerfile"
  tags       = target.foo.tags
}