Thrifty Builder

Builds Docker images, capturing information to reduce the frequency of future re-builds

Introduction

Thrifty builder stores a hash of all the ingredients that go into building a Docker image so the tool is able to determine if an image has already been built before, even if the build cache has been emptied or if the build is taking place on a different machine with a separate cache.

In our setup, we are building a large number of Docker images in our CI. The CI job runs on a different machine each time (with separate caches), meaning that if docker build was used, all images would be rebuild every time the CI runs. Pulling first would sped things up but it would require all images to be downloaded to the build machine first!

The aim is to minimise our CI run time and to keep our Docker images as stable as possible (it is usually extremely difficult to version everything that goes into an image so each re-build will create a slightly different image, even if the context and Dockerfile are the same).

Installation

Prerequisites

Docker (Server API version >= 1.21)
Python 3.6+

The tool can be installed from PyPi:

pip install thriftybuilder

Bleeding edge versions can be installed directly from GitHub:

pip install git+https://github.com/wtsi-hgi/thrifty-builder.git@master#egg=thriftybuilder

Usage

Configuration

A build configuration YAML file is required to use the tool. This file details the images that are to be built, the Docker registries to push the created images to (optional) and the location of the checksum storage.

Storage

stdin/stdout

(Default if not specified)

checksum_storage:
  type: stdio

Local

checksum_storage:
  type: local
  path: /root/.thrifty/checksums

Consul

checksum_storage:
  type: consul
  url: https://example.com:8500           # Optional: derived from Consul environment variables if not set
  token: "{{ env['CONSUL_HTTP_TOKEN'] }}"   # Optional: derived from Consul environment variables if not set
  key: ci/image-checksums
  lock: ci/image-checksums.lock

Note: to use Consul-backed storage, the requirements in consul_requirements.txt must be installed (not done so by default).

CLI

usage: thrifty [-h] [-v] [--built-only] configuration-location

Builds Docker images, capturing information to reduce the frequency of future
re-builds (v1.0.0b0)

positional arguments:
  configuration-location
                        location of configuration

optional arguments:
  -h, --help            show this help message and exit
  -v                    increase the level of log verbosity (add multiple
                        increase further)
  --built-only          only print details about newly built images on stdout

Example

configuration.yml

docker:
  images:
    - name: wtsi-hgi/image-1
      dockerfile: /images/image-1/Dockerfile
      context: /images
    - name: wtsi-hgi/image-2:version-1
      dockerfile: /images/image-2/Dockerfile
      # Context assumed to be /images/image-2 
  registries:
    - url: docker.io
      username: "{{ env['DOCKER_IO_USERNAME'] }}"
      password: "{{ env['DOCKER_IO_PASSWORD'] }}"
      
checksum_storage:
  type: consul
  url: "{{ env['CONSUL_HTTP_ADDR'] }}"
  token: "{{ env['CONSUL_HTTP_TOKEN'] }}"
  key: ci/image-checksums
  lock: ci/image-checksums.lock

CLI:

thrifty configuration.yml
{"wtsi-hgi/image-1": "b2db4c1ae978201407c69573ba89a9b8", "wtsi-hgi/image-2": "f9a4d7cc9f7133756b36973cc2d888de"}

Development

Setup

Install the tool's dependencies and the dependencies needed for testing:

pip install -U -r test_requirements.txt
pip install -U -r requirements.txt
pip install -U -r consul_requirements.txt

Testing

In the project directory, run:

PYTHONPATH=. python -m unittest discover -v -s thriftybuilder/tests

The CI runs the tests and generates coverage with run-tests.sh. This script runs the tests as described above in, addition to testing that the tool can be installed without errors.

To run the tests entirely in docker, use run-tests-in-docker.sh (experimental).

Alternatives

Share a build cache between all image building machines and make sure the cache is not lost.
More exotic Docker image builders might store information about the build context with the built image.

wtsi-hgi / thrifty-builder