About

GitHub Action to extract metadata (tags, labels) for Docker. This action is particularly useful if used with Docker Build Push action.

---

• Usage
  • Basic
  • Semver
  • Bake definition
• Customizing
  • inputs
  • outputs
• flavor input
• tags input
  • type=schedule
  • type=semver
  • type=match
  • type=edge
  • type=ref
  • type=raw
  • type=sha
• Notes
  • Latest tag
  • Global expressions
  • Major version zero
  • Overwrite labels
• Keep up-to-date with GitHub Dependabot

Usage

Basic

name: ci

on:
  push:
    branches:
      - 'master'
    tags:
      - 'v*'
  pull_request:
    branches:
      - 'master'

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      -
        name: Checkout
        uses: actions/checkout@v2
      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v3
        with:
          images: name/app
      -
        name: Login to DockerHub
        if: github.event_name != 'pull_request'
        uses: docker/login-action@v1
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}
      -
        name: Build and push
        uses: docker/build-push-action@v2
        with:
          context: .
          push: ${{ github.event_name != 'pull_request' }}
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}

Event	Ref	Docker Tags
pull_request	refs/pull/2/merge	pr-2
push	refs/heads/master	master
push	refs/heads/releases/v1	releases-v1
push tag	refs/tags/v1.2.3	v1.2.3, latest
push tag	refs/tags/v2.0.8-beta.67	v2.0.8-beta.67, latest

Semver

name: ci

on:
  push:
    branches:
      - 'master'
    tags:
      - 'v*'
  pull_request:
    branches:
      - 'master'

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      -
        name: Checkout
        uses: actions/checkout@v2
      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v3
        with:
          images: name/app
          tags: |
            type=ref,event=branch
            type=ref,event=pr
            type=semver,pattern={{version}}
            type=semver,pattern={{major}}.{{minor}}
      -
        name: Login to DockerHub
        if: github.event_name != 'pull_request'
        uses: docker/login-action@v1
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}
      -
        name: Build and push
        uses: docker/build-push-action@v2
        with:
          context: .
          push: ${{ github.event_name != 'pull_request' }}
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}

Event	Ref	Docker Tags
pull_request	refs/pull/2/merge	pr-2
push	refs/heads/master	master
push	refs/heads/releases/v1	releases-v1
push tag	refs/tags/v1.2.3	1.2.3, 1.2, latest
push tag	refs/tags/v2.0.8-beta.67	2.0.8-beta.67

Bake definition

This action also handles a bake definition file that can be used with the Docker Bake action. You just have to declare an empty target named docker-metadata-action and inherit from it.

// docker-bake.hcl
target "docker-metadata-action" {}

target "build" {
  inherits = ["docker-metadata-action"]
  context = "./"
  dockerfile = "Dockerfile"
  platforms = ["linux/amd64", "linux/arm/v6", "linux/arm/v7", "linux/arm64", "linux/386", "linux/ppc64le"]
}

name: ci

on:
  push:
    branches:
      - 'master'
    tags:
      - 'v*'

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      -
        name: Checkout
        uses: actions/checkout@v2
      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v3
        with:
          images: name/app
          tags: |
            type=ref,event=branch
            type=ref,event=pr
            type=semver,pattern={{version}}
            type=semver,pattern={{major}}.{{minor}}
            type=sha
      -
        name: Build
        uses: docker/bake-action@v1
        with:
          files: |
            ./docker-bake.hcl
            ${{ steps.meta.outputs.bake-file }}
          targets: build

Content of ${{ steps.meta.outputs.bake-file }} file will look like this with refs/tags/v1.2.3 ref:

{
  "target": {
    "docker-metadata-action": {
      "tags": [
        "name/app:1.2.3",
        "name/app:1.2",
        "name/app:sha-90dd603",
        "name/app:latest"
      ],
      "labels": {
        "org.opencontainers.image.title": "Hello-World",
        "org.opencontainers.image.description": "This your first repo!",
        "org.opencontainers.image.url": "https://github.com/octocat/Hello-World",
        "org.opencontainers.image.source": "https://github.com/octocat/Hello-World",
        "org.opencontainers.image.version": "1.2.3",
        "org.opencontainers.image.created": "2020-01-10T00:30:00.000Z",
        "org.opencontainers.image.revision": "90dd6032fac8bda1b6c4436a2e65de27961ed071",
        "org.opencontainers.image.licenses": "MIT"
      },
      "args": {
        "DOCKER_META_IMAGES": "name/app",
        "DOCKER_META_VERSION": "1.2.3"
      }
    }
  }
}

Customizing

inputs

Following inputs can be used as step.with keys

List type is a newline-delimited string

labels: |
  org.opencontainers.image.title=MyCustomTitle
  org.opencontainers.image.description=Another description
  org.opencontainers.image.vendor=MyCompany

CSV type is a comma-delimited string

images: name/app,ghcr.io/name/app

Name	Type	Description
images	List/CSV	List of Docker images to use as base name for tags
tags	List	List of tags as key-value pair attributes
flavor	List	Flavor to apply
labels	List	List of custom labels
sep-tags	String	Separator to use for tags output (default \n)
sep-labels	String	Separator to use for labels output (default \n)
bake-target	String	Bake target name (default docker-metadata-action)

outputs

Following outputs are available

Name	Type	Description
version	String	Docker image version
tags	String	Docker tags
labels	String	Docker labels
bake-file	File	Bake definition file path

flavor input

flavor defines a global behavior for tags:

flavor: |
  latest=auto
  prefix=
  suffix=

• latest=<auto|true|false>: Handle latest tag (default auto)
• prefix=<string>: A global prefix for each generated tag
• suffix=<string>: A global suffix for each generated tag

tags input

tags is the core input of this action as everything related to it will reflect the output metadata. This one is in the form of a key-value pair list in CSV format to remove limitations intrinsically linked to GitHub Actions (only string format is handled in the input fields). Here is an example:

tags: |
  type=schedule
  type=ref,event=branch
  type=ref,event=pr
  type=semver,pattern={{version}}
  type=semver,pattern={{major}}.{{minor}}
  type=semver,pattern={{major}}
  type=sha

Each entry is defined by a type, which are:

• type=schedule
• type=semver
• type=match
• type=edge
• type=ref
• type=raw
• type=sha

And global attributes:

• enable=<true|false> enable this entry (default true)
• priority=<number> priority to manage the order of tags
• prefix=<string> add prefix
• suffix=<string> add suffix

Default entries if tags input is empty:

tags: |
  type=schedule
  type=ref,event=branch
  type=ref,event=tag
  type=ref,event=pr

type=schedule

tags: |
  # minimal
  type=schedule
  # default
  type=schedule,pattern=nightly
  # handlebars
  type=schedule,pattern={{date 'YYYYMMDD'}}

Will be used on schedule event.

pattern is a specially crafted attribute to support Handlebars template with the following expressions:

• date 'format' ; render date by its moment format

Pattern	Output
nightly	nightly
{{date 'YYYYMMDD'}}	20210326

Extended attributes and default values:

tags: |
  type=schedule,enable=true,priority=1000,prefix=,suffix=,pattern=nightly

type=semver

tags: |
  # minimal
  type=semver,pattern={{version}}
  # use custom value instead of git tag
  type=semver,pattern={{version}},value=v1.0.0

Will be used on a push tag event and requires a valid Git tag semver but you can also use a custom value through value attribute.

pattern attribute supports Handlebars template with the following expressions:

• raw ; the actual semver
• version ; shorthand for {{major}}.{{minor}}.{{patch}} (can include pre-release)
• major ; major version identifier
• minor ; minor version identifier
• patch ; patch version identifier

Git tag	Pattern	Output
v1.2.3	{{raw}}	v1.2.3
v1.2.3	{{version}}	1.2.3
v1.2.3	{{major}}.{{minor}}	1.2
v1.2.3	v{{major}}	v1
v1.2.3	{{minor}}	2
v1.2.3	{{patch}}	3
v2.0.8-beta.67	{{raw}}	2.0.8-beta.67*
v2.0.8-beta.67	{{version}}	2.0.8-beta.67
v2.0.8-beta.67	{{major}}.{{minor}}	2.0.8-beta.67*

*Pre-release (rc, beta, alpha) will only extend {{version}} as tag because they are updated frequently, and contain many breaking changes that are (by the author's design) not yet fit for public consumption.

Extended attributes and default values:

tags: |
  type=semver,enable=true,priority=900,prefix=,suffix=,pattern=,value=

type=match

tags: |
  # minimal
  type=match,pattern=\d.\d.\d
  # define match group
  type=match,pattern=v(.*),group=1
  # use custom value instead of git tag
  type=match,pattern=v(.*),group=1,value=v1.0.0

Can create a regular expression for matching Git tag with a pattern and capturing group. Will be used on a push tag event but you can also use a custom value through value attribute.

Git tag	Pattern	Group	Output
v1.2.3	\d.\d.\d	0	1.2.3
v2.0.8-beta.67	v(.*)	1	2.0.8-beta.67
v2.0.8-beta.67	v(\d.\d)	1	2.0
20200110-RC2	\d+	0	20200110
p1/v1.2.3	p1-v(\d.\d.\d)	1	1.2.3

Extended attributes and default values:

tags: |
  type=match,enable=true,priority=800,prefix=,suffix=,pattern=,group=0,value=

type=edge

tags: |
  # minimal
  type=edge
  # define default branch
  type=edge,branch=main

An edge tag reflects the last commit of the active branch on your Git repository. I usually prefer to use edge as a Docker tag for a better distinction or common pattern. This is also used by official images like Alpine.

Extended attributes and default values:

tags: |
  type=edge,enable=true,priority=700,prefix=,suffix=,branch=$repo.default_branch

type=ref

tags: |
  # branch event
  type=ref,event=branch
  # tag event
  type=ref,event=tag
  # pull request event
  type=ref,event=pr

This type handles Git ref (or reference) for the following events:

• branch ; eg. refs/heads/master
• tag ; eg. refs/tags/v1.0.0
• pr ; eg. refs/pull/318/merge

Event	Ref	Output
pull_request	refs/pull/2/merge	pr-2
push	refs/heads/master	master
push	refs/heads/my/branch	my-branch
push tag	refs/tags/v1.2.3	v1.2.3
push tag	refs/tags/v2.0.8-beta.67	v2.0.8-beta.67

Extended attributes and default values:

tags: |
  # branch event
  type=ref,enable=true,priority=600,prefix=,suffix=,event=
  # tag event
  type=ref,enable=true,priority=600,prefix=,suffix=,event=
  # pull request event
  type=ref,enable=true,priority=600,prefix=pr-,suffix=,event=

type=raw

tags: |
  type=raw,value=foo
  type=raw,value=bar
  # or
  type=raw,foo
  type=raw,bar
  # or
  foo
  bar

Output custom tags according to your needs.

Extended attributes and default values:

tags: |
  type=raw,enable=true,priority=200,prefix=,suffix=,value=

type=sha

tags: |
  # minimal
  type=sha

tags: |
  # minimal using short sha
  type=sha
  # full length sha
  type=sha,format=long

Output Git short commit (or long if specified) as Docker tag like sha-ad132f5.

Extended attributes and default values:

tags: |
  type=sha,enable=true,priority=100,prefix=sha-,suffix=,format=short

Notes

Latest tag

latest tag is handled through the flavor input. It will be generated by default (auto mode) for:

• type=ref,event=tag
• type=semver,pattern=...
• type=match,pattern=...

Global expressions

The following Handlebars template expressions for prefix, suffix and value attributes are available:

Expression	Output
{{branch}}	master
{{tag}}	v1.2.3
{{sha}}	90dd603

tags: |
  # dynamically set the branch name as a prefix
  type=sha,prefix={{branch}}-
  # dynamically set the branch name and sha as a custom tag
  type=raw,value=mytag-{{branch}}-{{sha}}

Major version zero

Major version zero (0.y.z) is for initial development and may change at any time. This means the public API should not be considered stable.

In this case, Docker tag 0 should not be generated if you're using type=semver with {{major}} pattern. You can manage this behavior like this:

# refs/tags/v0.1.2
tags: |
  # output 0.1.2
  type=semver,pattern={{version}}
  # output 0.1
  type=semver,pattern={{major}}.{{minor}}
  # disabled if major zero
  type=semver,pattern={{major}},enable=${{ !startsWith(github.ref, 'refs/tags/v0.') }}

Overwrite labels

If some of the OCI Image Format Specification labels generated are not suitable, you can overwrite them like this:

      -
        name: Docker meta
        id: docker_meta
        uses: docker/metadata-action@v3
        with:
          images: name/app
          labels: |
            maintainer=CrazyMax
            org.opencontainers.image.title=MyCustomTitle
            org.opencontainers.image.description=Another description
            org.opencontainers.image.vendor=MyCompany

Keep up-to-date with GitHub Dependabot

Since Dependabot has native GitHub Actions support, to enable it on your GitHub repo all you need to do is add the .github/dependabot.yml file:

version: 2
updates:
  # Maintain dependencies for GitHub Actions
  - package-ecosystem: "github-actions"
    directory: "/"
    schedule:
      interval: "daily"