Kaniko image builder

This Action uses the kaniko executor instead of the docker daemon. Kaniko builds the image by extracting the filesystem of the base image, making the changes in the user space, snapshotting any change and appending it to the base image filesystem.

This allows for a quite efficient caching, that can be pushed to another docker registry and downloaded on-demand, and a noticeably easier and more secure secret passing to the build context, as it happens in the user space itself.

Usage

Example pipeline

name: Docker build
on: push
jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@master
      - name: Kaniko build
        uses: aevea/action-kaniko@master
        with:
          image: aevea/kaniko
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_PASSWORD }}
          cache: true
          cache_registry: aevea/cache

Required Arguments

This action aims to be as flexible as possible, so it tries to define the defaults as for what I thought of being the most used values. So, technically there is a single required argument

variable	description	required	default
image	Name of the image you would like to push	true

Optional Arguments

variable	description	required	default
registry	Docker registry where the image will be pushed	false	docker.io
username	Username used for authentication to the Docker registry	false	$GITHUB_ACTOR
password	Password used for authentication to the Docker registry	false
tag	Image tag	false	latest
cache	Enables build cache	false	false
cache_ttl	How long the cache should be considered valid	false
cache_registry	Docker registry meant to be used as cache	false
cache_directory	Filesystem path meant to be used as cache	false
build_file	Dockerfile filename	false	Dockerfile
extra_args	Additional arguments to be passed to the kaniko executor	false
strip_tag_prefix	Prefix to be stripped from the tag	false
skip_unchanged_digest	Avoids pushing the image if the build generated the same digest	false
path	Path to the build context. Defaults to .	false	.
tag_with_latest	Tags the built image with additional latest tag	false
target	Sets the target stage to build	false
debug	Enables trace for entrypoint.sh	false

Here is where it gets specific, as the optional arguments become required depending on the registry targeted

docker.io

This is the default, and implicit docker registry, in the same way as with using the docker CLI In this case, the authentication credentials need to be passed via GitHub Action secrets

with:
  image: aevea/kaniko
  username: ${{ secrets.DOCKERHUB_USERNAME }}
  password: ${{ secrets.DOCKERHUB_PASSWORD }}

NOTE: Dockerhub doesn't support more than one level deep of docker images, so Kaniko's default approach of pushing the cache to $image/cache doesn't work. If you want to use caching with Dockerhub, create a cache repository, and specify it in the action options.

with:
  image: aevea/kaniko
  username: ${{ secrets.DOCKERHUB_USERNAME }}
  password: ${{ secrets.DOCKERHUB_PASSWORD }}
  cache: true
  cache_registry: aevea/cache

ghcr.io

GitHub's docker registry is a bit special. It doesn't allow top-level images, so this action will prefix any image with the GitHub namespace. If you want to push your image like aevea/action-kaniko/kaniko, you'll only need to pass kaniko to this action.

The authentication is automatically done using the GITHUB_ACTOR and GITHUB_TOKEN provided from GitHub itself. But as GITHUB_TOKEN is not passed by default, it will have to be explicitly set up.

with:
  registry: ghcr.io
  password: ${{ secrets.GITHUB_TOKEN }}
  image: kaniko

NOTE: GitHub's docker registry is structured a bit differently, but it has the same drawback as Dockerhub, and that's that it's not possible to "namespace" images for cache. In order to use registry cache, just specify the image meant to be used as cache, and Kaniko will push the cache layers to that image instead

with:
  registry: ghcr.io
  password: ${{ secrets.GITHUB_TOKEN }}
  image: kaniko
  cache: true
  cache_registry: cache

registry.gitlab.com

GitLab's registry is quite flexible, it allows easy image namespacing, so a project's docker registry can hold up to three levels of image repository names.

registry.gitlab.com/group/project:some-tag
registry.gitlab.com/group/project/image:latest
registry.gitlab.com/group/project/my/image:rc1

To authenticate to it, a username and personal access token must be supplied via GitHub Action Secrets.

with:
  registry: registry.gitlab.com
  username: ${{ secrets.GL_REGISTRY_USERNAME }}
  password: ${{ secrets.GL_REGISTRY_PASSWORD }}
  image: aevea/kaniko

NOTE: As GitLab's registry does support namespacing, Kaniko can natively push cached layers to it, so only cache: true is necessary to be specified in order to use it.

with:
  registry: registry.gitlab.com
  username: ${{ secrets.GL_REGISTRY_USERNAME }}
  password: ${{ secrets.GL_REGISTRY_PASSWORD }}
  image: aevea/kaniko
  cache: true

Other registries

If you would like to publish the image to other registries, these actions might be helpful

Registry	Action
Amazon Webservices Elastic Container Registry (ECR)	https://github.com/elgohr/ecr-login-action
Google Cloud Container Registry	https://github.com/elgohr/gcloud-login-action

Other arguments details

tag

The tag argument, unless overridden, is automatically guessed based on the branch name. If the branch is master then the tag will be latest, otherwise it will keep the branch name, but replacing any forward slash (/) with a hyphen (-).

If the v prefix that it's usually added to the GitHub releases is not desired when pushed to dockerhub, the strip_tag_prefix allows to specify which part of the tag should be removed.

Example:

with:
  registry: ghcr.io
  password: ${{ secrets.GITHUB_TOKEN }}
  image: kaniko
  strip_tag_prefix: pre-

for the tag pre-0.1 will push kaniko:0.1, as the pre- part will be stripped from the tag name.

Outputs

image

Full reference to the built image with registry and tag.