Docker ECR Cache Buildkite Plugin

A Buildkite plugin to cache Docker images in Amazon ECR.

This allows you to define a Dockerfile for your build-time dependencies without worrying about the time it takes to build the image. It allows you to re-use entire Docker images without worrying about layer caching, and/or pruning layers as changes are made to your containers.

An ECR repository to store the built Docker image will be created for you, if one doesn't already exist.

Example

Basic usage

FROM bash

RUN echo "my expensive build step"

steps:
  - command: 'echo wow'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0
      - docker#v3.3.0

Caching npm packages

This plugin can be used to effectively cache node_modules between builds without worrying about Docker layer cache invalidation. You do this by hinting when the image should be re-built.

FROM node:10-alpine

WORKDIR /workdir

COPY package.json package-lock.json /workdir

# this step downloads the internet
RUN npm install

steps:
  - command: 'npm test'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          cache-on:
            - package-lock.json
      - docker#v3.3.0:
          volumes:
            - /workdir/node_modules

The cache-on property also supports Bash globbing with globstar:

steps:
  - command: 'npm test'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          cache-on:
            - '**/package.json' # monorepo with multiple manifest files
            - yarn.lock
      - docker#v3.0.1:
          volumes:
            - /workdir/node_modules

Using another Dockerfile

It's possible to specify the Dockerfile to use by:

steps:
  - command: 'echo wow'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          dockerfile: my-dockerfile
      - docker#v3.3.0

The subdirectory containing the Dockerfile is the path used for the build's context.

Specifying a target step

A multi-stage Docker build can be used to reduce an application container to just its runtime dependencies. However, this stripped down container may not have the environment necessary for running CI commands such as tests or linting. Instead, the target property can be used to specify an intermediate build stage to run commands against:

steps:
  - command: 'cargo test'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          target: build-deps
      - docker#v3.3.0

Specifying build args

Build-time variables are supported, either with an explicit value, or without one to propagate an environment variable from the pipeline step:

FROM bash

ARG ARG_1
ARG ARG_2

RUN echo "${ARG_1}"
RUN echo "${ARG_2}"

steps:
  - command: 'echo amaze'
    env:
      ARG_1: wow
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          build-args:
            - ARG_1
            - ARG_2=such
      - docker#v3.3.0

Additional docker build arguments be passed via the additional-build-args setting:

steps:
  - command: 'echo amaze'
    env:
      ARG_1: wow
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          additional-build-args: '--ssh= default=\$SSH_AUTH_SOCK'
      - docker#v3.3.0

Specifying an ECR repository name

The plugin pushes and pulls Docker images to and from an ECR repository named build-cache/${BUILDKITE_ORGANIZATION_SLUG}/${BUILDKITE_PIPELINE_SLUG}. You can optionally use a custom repository name:

steps:
  - command: 'echo wow'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          ecr-name: my-unique-repository-name
          ecr-tags: 
            Key: Value
            Key2: Value2
      - docker#v3.3.0

Changing the max cache time

By default images are kept in ECR for up to 30 days. This can be changed by specifying a max-age-days parameter:

steps:
  - command: 'echo wow'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          max-age-days: 7
      - docker#v3.3.0

Changing the name of exported variable

By default image name and computed tag are exported to the Docker buildkite plugin env variable BUILDKITE_PLUGIN_DOCKER_IMAGE. In order to chain the plugin with a different plugin, this can be changed by specifying a export-env-variable parameter:

steps:
  - command: 'echo wow'
    plugins:
      - seek-oss/docker-ecr-cache#v1.7.0:
          export-env-variable: BUILDKITE_PLUGIN_MY_CUSTOM_PLUGIN_CACHE_IMAGE
      - my-custom-plugin#v1.0.0

Design

The plugin derives a checksum from:

• The argument names and values specified in the build-args property
• The files specified in the cache-on and dockerfile properties

This checksum is used as the Docker image tag to find and pull an existing cached image from ECR, or to build and push a new image for subsequent builds to use.

The plugin handles the creation of a dedicated ECR repository for the pipeline it runs in. To save on ECR storage costs and give images a chance to update/patch, a lifecycle policy is automatically applied to expire images after 30 days (configurable via max-age-days).

Tests

To run the tests of this plugin, run

docker-compose run --rm tests

License

MIT (see LICENSE)