# Kaniko image builder

This Action uses the [kaniko](https://github.com/GoogleContainerTools/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
```yaml
name: Docker build
on: push
jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@master
      - name: Kaniko build
        uses: outillage/kaniko-action@master
        with:
          image: outillage/kaniko
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_PASSWORD }}
          cache: true
          cache_registry: outillage/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    |                             |

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

### [docker.io](https://hub.docker.com/)

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

```yaml
with:
  image: outillage/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.

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

### [docker.pkg.github.com](https://github.com/features/packages)

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 `outillage/kaniko-action/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.

```yaml
with:
  registry: docker.pkg.github.com
  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

```yaml
with:
  registry: docker.pkg.github.com
  password: ${{ secrets.GITHUB_TOKEN }}
  image: kaniko
  cache: true
  cache_registry: cache
```

### [registry.gitlab.com](https://docs.gitlab.com/ee/user/packages/container_registry)

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.

```yaml
with:
  registry: registry.gitlab.com
  username: ${{ secrets.GL_REGISTRY_USERNAME }}
  password: ${{ secrets.GL_REGISTRY_PASSWORD }}
  image: outillage/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.

```yaml
with:
  registry: registry.gitlab.com
  username: ${{ secrets.GL_REGISTRY_USERNAME }}
  password: ${{ secrets.GL_REGISTRY_PASSWORD }}
  image: outillage/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:

```yaml
with:
  registry: docker.pkg.github.com
  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.