Boatswain is a simple build system for docker images.

It is especially useful when you have multiple docker images that depend on each other.

Boatswain is a simple python script you can install with pip

$ pip install boatswain

Create a file called boatswain.yml for your project with the following syntax, which is heavily based on docker-compose.

version: 1.0                    # The version of the boatswain yaml
organisation: boatswain         # Your dockerhub organisation
images:
    image1:pytest:              # the key will be used to tag the image
        context: docker/image1  # The path of the dockerfile
    image2:pytest:
        context: docker/image2
        from: image1:pytest     # This image depends on the other image
    image3:pytest:
        context: docker/image3
        from: image2:pytest
    image4:pytest:
        context: docker/image4
        tag: image12:pytest     # This image will be tagged with this

You can build the images defined in the boatswain file using the following command. This invokes the docker build process for each image in the order so the dependencies are built before the dependent image.

$ boatswain build

You can clean the images that are defined in the boatswain file.

$ boatswain clean

You can push the built images to dockerhub using the push command. It will be pushed to organisation/imagetag on dockerhub.

$ boatswain push

When your build does not go the way you expected boatswain can display some more information by using: