support using local image tarballs with FROM

[vito]

This adds 'image args', configurable with IMAGE_ARG_* - similar to BUILD_ARG_*, only the value points to an image tarball.

The image tarball will be loaded and served by a local registry, and a reference to the image in the local registry will be provided as the build arg.

To use this, you must modify your Dockerfile like so:

ARG base_image=ubuntu
FROM ${base_image}

Then, when running oci-build-task, specify:

params:
  IMAGE_ARG_base_image: ubuntu/image.tar

This will remain forward compatible if we ever switch to Kaniko (#46), which would also require using build args as Kaniko image caching requires a full digest to be specified in FROM.

fixes #1
closes #2
closes #3
closes #14

[vito]

just FYI: seeing issues with this, reproducible in a local test but haven't found the root cause yet. building works fine but the resulting image seems corrupt in some way (fails with unexpected EOF when trying to unpack). will ship this as soon as I figure that out.

[vito]

just FYI: seeing issues with this, reproducible in a local test but haven't found the root cause yet. building works fine but the resulting image seems corrupt in some way (fails with unexpected EOF when trying to unpack). will ship this as soon as I figure that out.

fixed in f4c893c

[cpadgett-comcast]

For those who end up here, there are some gotchas to the solution above:

1. The variable name used for FROM ${base_image} must be all lowercase, otherwise the build will fail with an error similar to failed to parse stage name "localhost:34785/DOCKERFILE_FROM_IMAGE": invalid reference format: repository name must be lowercase

2. The FROM image being used locally must specify the parameter format: oci, otherwise the build will fail with an error similar to failed to build: create local image registry: image from path: open base-image/image.tar: no such file or directory

3. The FROM image must be an input to the task, otherwise you will get the same error as 2 above.

4. The outputs for the image building task must be image, otherwise the build will fail with an error similar to no files match glob 'some-mistaken-output-image-name/image.tar'

Example pipeline

build-docker-image.yaml

---
platform: linux

image_resource:
  type: registry-image
  source:
    repository: concourse/oci-build-task

inputs:
- name: image-src
  path: .
- name: docker-from-image

outputs:
- name: image

run:
  path: build

Dockerfile

ARG  dockerfile_from_image=repository/url/path/image:tag
FROM ${dockerfile_from_image}

<more-dockerfile-stuff>

pipeline.yaml

resources:
- name: concourse-tasks-repo
  type: git
  source:
    uri: ((concourse_tasks_repo))
    branch: ((concourse_tasks_release_branch))

- name: tools-image-source-repo
  type: git
  source:
    uri: ((tools_image_src_repo))
    branch: ((tools_image_src_release_branch))

- name: tools-from-image
  type: registry-image
  source:
    repository: "((tools_from_image_docker_repo))"
    username: ((dockerregistry.username))  # store your secrets in a secrets manager like Vault
    password: ((dockerregistry.password))  # store your secrets in a secrets manager like Vault

- name: tools-image
  type: registry-image
  source:
    repository: "((tools_image_docker_repo))"
    username: ((dockerregistry.username))  # store your secrets in a secrets manager like Vault
    password: ((dockerregistry.password))  # store your secrets in a secrets manager like Vault

jobs:
- name: build-and-push-tools-image
  plan:
  - in_parallel:
      fail_fast: true
      steps:
      - get: concourse-tasks-repo
        trigger: true
      - get: tools-from-image
        params:
          format: oci
        trigger: true

  - task: build-tools-image
    privileged: true
    file: "concourse-tasks-repo/build-docker-image.yml"
    input_mapping:
      docker-from-image: tools-from-image
      image-src: tools-image-source-repo
    output_mapping:
      image: built-tools-image
    params:
      IMAGE_ARG_dockerfile_from_image: docker-from-image/image.tar

  - put: tools-image
    params:
      image: built-tools-image/image.tar