Building with Bake from a Compose file

Specification

Bake uses the compose-spec to parse a compose file and translate each service to a target.

# docker-compose.yml
services:
  webapp-dev:
    build: &build-dev
      dockerfile: Dockerfile.webapp
      tags:
        - docker.io/username/webapp:latest
      cache_from:
        - docker.io/username/webapp:cache
      cache_to:
        - docker.io/username/webapp:cache

  webapp-release:
    build:
      <<: *build-dev
      x-bake:
        platforms:
          - linux/amd64
          - linux/arm64

  db:
    image: docker.io/username/db
    build:
      dockerfile: Dockerfile.db
$ docker buildx bake --print

{
  "group": {
    "default": {
      "targets": ["db", "webapp-dev", "webapp-release"]
    }
  },
  "target": {
    "db": {
      "context": ".",
      "dockerfile": "Dockerfile.db",
      "tags": ["docker.io/username/db"]
    },
    "webapp-dev": {
      "context": ".",
      "dockerfile": "Dockerfile.webapp",
      "tags": ["docker.io/username/webapp:latest"],
      "cache-from": ["docker.io/username/webapp:cache"],
      "cache-to": ["docker.io/username/webapp:cache"]
    },
    "webapp-release": {
      "context": ".",
      "dockerfile": "Dockerfile.webapp",
      "tags": ["docker.io/username/webapp:latest"],
      "cache-from": ["docker.io/username/webapp:cache"],
      "cache-to": ["docker.io/username/webapp:cache"],
      "platforms": ["linux/amd64", "linux/arm64"]
    }
  }
}

The compose format has some limitations compared to the HCL format:

  • Specifying variables or global scope attributes is not yet supported
  • inherits service field is not supported, but you can use YAML anchors to reference other services, as demonstrated in the previous example with &build-dev.

.env file

You can declare default environment variables in an environment file named .env. This file will be loaded from the current working directory, where the command is executed and applied to compose definitions passed with -f.

# docker-compose.yml
services:
  webapp:
    image: docker.io/username/webapp:${TAG:-v1.0.0}
    build:
      dockerfile: Dockerfile
# .env
TAG=v1.1.0
$ docker buildx bake --print

{
  "group": {
    "default": {
      "targets": ["webapp"]
    }
  },
  "target": {
    "webapp": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": ["docker.io/username/webapp:v1.1.0"]
    }
  }
}

Note

System environment variables take precedence over environment variables in .env file.

Extension field with x-bake

Where some fields are not available in the compose specification, you can use the special extension field x-bake in your compose file to evaluate extra fields:

# docker-compose.yml
services:
  addon:
    image: ct-addon:bar
    build:
      context: .
      dockerfile: ./Dockerfile
      args:
        CT_ECR: foo
        CT_TAG: bar
      x-bake:
        tags:
          - ct-addon:foo
          - ct-addon:alp
        platforms:
          - linux/amd64
          - linux/arm64
        cache-from:
          - user/app:cache
          - type=local,src=path/to/cache
        cache-to:
          - type=local,dest=path/to/cache
        pull: true

  aws:
    image: ct-fake-aws:bar
    build:
      dockerfile: ./aws.Dockerfile
      args:
        CT_ECR: foo
        CT_TAG: bar
      x-bake:
        secret:
          - id=mysecret,src=./secret
          - id=mysecret2,src=./secret2
        platforms: linux/arm64
        output: type=docker
        no-cache: true
$ docker buildx bake --print

{
  "group": {
    "default": {
      "targets": ["aws", "addon"]
    }
  },
  "target": {
    "addon": {
      "context": ".",
      "dockerfile": "./Dockerfile",
      "args": {
        "CT_ECR": "foo",
        "CT_TAG": "bar"
      },
      "tags": ["ct-addon:foo", "ct-addon:alp"],
      "cache-from": ["user/app:cache", "type=local,src=path/to/cache"],
      "cache-to": ["type=local,dest=path/to/cache"],
      "platforms": ["linux/amd64", "linux/arm64"],
      "pull": true
    },
    "aws": {
      "context": ".",
      "dockerfile": "./aws.Dockerfile",
      "args": {
        "CT_ECR": "foo",
        "CT_TAG": "bar"
      },
      "tags": ["ct-fake-aws:bar"],
      "secret": ["id=mysecret,src=./secret", "id=mysecret2,src=./secret2"],
      "platforms": ["linux/arm64"],
      "output": ["type=docker"],
      "no-cache": true
    }
  }
}

Complete list of valid fields for x-bake:

  • cache-from
  • cache-to
  • contexts
  • no-cache
  • no-cache-filter
  • output
  • platforms
  • pull
  • secret
  • ssh
  • tags