Boatswain

Boatswain is a simple build system for docker images.

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

Installation

Boatswain is a simple python script you can install with pip

$ pip install boatswain

Usage

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

Building

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

Cleaning

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

$ boatswain clean

Pushing

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

$ boatswain push

Extra Options

-h	Display the options
-q, --quiet	Don't display any output
-k, --keep_building
	Keep building images even if an error occurs
--dryrun	Do not actually execute the command, just go through the motions
-b <boatswain_file>, --boatswain_file <boatswain_file>
	Override the default boatswain file (boatswain.yml)
-f, --force	Force building the images, even if they already exist (only for build)

Debugging your build

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

-v	Verbose mode, displays a build progress for each image
-vv	Very verbose mode, displays the output of the docker build process
--debug	Debug mode, displays debug information of boatswain as well as the output of the docker build process