Experiment to build a docker builder image that includes only static docker binaries, using Bazel

BUILD

load(                                                
    "@io_bazel_rules_docker//docker:docker.bzl",
    "docker_build",
)                        
                    
docker_build(
    name = "target",                                                                                                                                                                                                
    base = "@base_image//image:image.tar",                                                                                                                                                                          
    directory = "/bin",                                                                                                                                                                                             
    entrypoint = ["/bin/docker"],                                                                                                                                                                                   
    files = ["@docker_static//:docker_static"],                                                                                                                                                                     
    mode = "0777",                                                                                                                                                                                                  
)

BUILD.docker

package(default_visibility = ["//visibility:public"])

filegroup(
  name = "docker_static",
  srcs = ["docker"],
)

cloudbuild.yaml

steps:
- name: 'gcr.io/cloud-builders/bazel'
  args: ['run', '//src:target', '--verbose_failures']
    
# Retag to desired image name.
- name: 'gcr.io/cloud-builders/docker'
  args: ['tag', 'bazel:target', 'gcr.io/$PROJECT_ID/docker-via-bazel']
    
# Sanity check.
- name: 'gcr.io/$PROJECT_ID/docker-via-bazel'
  args: ['run', 'hello-world']
    
images:                                                                                                                                                                                                             
- 'gcr.io/$PROJECT_ID/docker-via-bazel'

WORKSPACE

workspace(name = "bazel_docker")                     
    
git_repository(
    name = "io_bazel_rules_docker",
    remote = "https://github.com/bazelbuild/rules_docker.git",
    tag = "v0.3.0",
)   
    
load(
    "@io_bazel_rules_docker//docker:docker.bzl",                                                                                                                                                                    
    "docker_pull",
    "docker_repositories",                                                                                                                                                                                          
)                                                                                                                                                                                                                   

# Consumers shouldn't need to do this themselves once WORKSPACE is
# instantiated recursively.
docker_repositories()

docker_pull(
    name = "base_image",
    registry = "launcher.gcr.io",
    repository = "google/ubuntu16_04",
    tag = "latest",  # TODO: use digest.
)

new_http_archive(
    name = "docker_static",
    build_file = "BUILD.docker",
    # TODO: specify SHA256.
    strip_prefix = "docker",
    type = "tgz",
    urls = ["https://download.docker.com/linux/static/stable/x86_64/docker-17.12.0-ce.tgz"],
)