About

GitHub Action to extract metadata from Git reference and GitHub events. This action is particularly useful if used with Docker Build Push action to tag and label Docker images.

---

• Usage
  • Basic
  • Semver
  • Bake definition
• Customizing
  • inputs
  • outputs
  • environment variables
• context input
• images input
• flavor input
• tags input
  • type=schedule
  • type=semver
  • type=pep440
  • type=match
  • type=edge
  • type=ref
  • type=raw
  • type=sha
• Notes
  • Image name and tag sanitization
  • Latest tag
  • priority attribute
  • Global expressions
    • {{branch}}
    • {{tag}}
    • {{sha}}
    • {{base_ref}}
    • {{is_default_branch}}
    • {{date '<format>' tz='<timezone>'}}
  • Major version zero
  • JSON output object
  • Overwrite labels
• Contributing

Usage

Basic

name: ci

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

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      -
        name: Checkout
        uses: actions/checkout@v3
      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v4
        with:
          images: name/app
      -
        name: Login to DockerHub
        if: github.event_name != 'pull_request'
        uses: docker/login-action@v2
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}
      -
        name: Build and push
        uses: docker/build-push-action@v4
        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
workflow_dispatch	refs/heads/master	master

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@v3
      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v4
        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@v2
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}
      -
        name: Build and push
        uses: docker/build-push-action@v4
        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"
  ]
}

name: ci

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

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      -
        name: Checkout
        uses: actions/checkout@v3
      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v4
        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@v2
        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": "860c1904a1ce19322e91ac35af1ab07466440c37",
        "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  

Name	Type	Description
context	String	Where to get context data. Allowed options are: workflow (default), git.
images	List	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
json	String	JSON output of tags and labels
bake-file	File	Bake file definition path

Alternatively, each output is also exported as an environment variable:

• DOCKER_METADATA_OUTPUT_VERSION
• DOCKER_METADATA_OUTPUT_TAGS
• DOCKER_METADATA_OUTPUT_LABELS
• DOCKER_METADATA_OUTPUT_JSON
• DOCKER_METADATA_OUTPUT_BAKE_FILE

So it can be used with our Docker Build Push action:

- uses: docker/build-push-action@v4
  with:
    build-args: |
      DOCKER_METADATA_OUTPUT_JSON      

environment variables

Name	Type	Description
DOCKER_METADATA_PR_HEAD_SHA	Bool	If true, set associated head SHA instead of commit SHA that triggered the workflow on pull request event

context input

context defines where to get context metadata:

# default
context: workflow
# or
context: git

• workflow: Get context metadata from the workflow (GitHub context). See https://docs.github.com/en/actions/learn-github-actions/contexts#github-context
• git: Get context metadata from the workflow and overrides some of them with current Git context, such as ref and sha.

images input

images defines a list of Docker images to use as base name for tags:

images: |
  name/foo
  ghcr.io/name/bar
  # or
  name=name/foo
  name=ghcr.io/name/bar  

Extended attributes and default values:

images: |
  name=,enable=true  

• name=<string> image base name
• enable=<true|false> enable this entry (default true)

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>,onlatest=<true|false>: A global prefix for each generated tag and optionally for latest
• suffix=<string>,onlatest=<true|false>: A global suffix for each generated tag and optionally for latest

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

Each entry is defined by a type, which are:

• type=schedule
• type=semver
• type=pep440
• type=match
• type=edge
• type=ref
• type=raw
• type=sha

And global attributes:

• enable=<true|false> enable this entry (default true)
• priority=<number> set tag priority order
• 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'}}
  # handlebars with timezone
  type=schedule,pattern={{date 'YYYYMMDD-hhmmss' tz='Asia/Tokyo'}}  

Will be used on schedule event.

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

• date 'format' tz='Timezone' ; render date by its moment format. Default tz is UTC.

Pattern	Output
nightly	nightly
{{date 'YYYYMMDD'}}	20200110
{{date 'YYYYMMDD-HHmmss' tz='Asia/Tokyo'}}	20200110-093000

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 semver Git tag, but you can also use a custom value through value attribute.

pattern attribute supports Handlebars template with the following expressions:

• raw ; the actual tag
• 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}}	v2.0.8-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}} (or {{raw}} if specified) 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=pep440

tags: |
  # minimal
  type=pep440,pattern={{version}}
  # use custom value instead of git tag
  type=pep440,pattern={{version}},value=1.0.0  

Will be used on a push tag event and requires a Git tag that conforms to PEP 440, but you can also use a custom value through value attribute.

pattern attribute supports Handlebars template with the following expressions:

• raw ; the actual tag
• version ; cleaned version
• major ; major version identifier
• minor ; minor version identifier
• patch ; patch version identifier

Git tag	Pattern	Output
1.2.3	{{raw}}	1.2.3
1.2.3	{{version}}	1.2.3
v1.2.3	{{version}}	1.2.3
1.2.3	{{major}}.{{minor}}	1.2
1.2.3	v{{major}}	v1
v1.2.3rc2	{{raw}}	v1.2.3rc2
1.2.3rc2	{{version}}	1.2.3rc2
1.2.3rc2	{{major}}.{{minor}}	1.2.3rc2*
1.2.3post1	{{major}}.{{minor}}	1.2.3.post1*
1.2.3beta2	{{major}}.{{minor}}	1.2.3b2*
1.0dev4	{{major}}.{{minor}}	1.0.dev4*

*dev/pre/post release will only extend {{version}} (or {{raw}} if specified) 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=pep440,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
workflow_dispatch	refs/heads/master	master

Extended attributes and default values:

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

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 (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

Image name and tag sanitization

In order to comply with the specification, the image name components may contain lowercase letters, digits and separators. A separator is defined as a period, one or two underscores, or one or more dashes. A name component may not start or end with a separator.

A tag name must be a valid ASCII chars sequences and may contain lowercase and uppercase letters, digits, underscores, periods and dashes. A tag name may not start with a period or a dash and may contain a maximum of 128 characters.

To ease the integration in your workflow, this action will automatically:

• Lowercase the image name
• Replace invalid chars sequences with - for tags

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=...

For conditionally tagging with latest for a specific branch name, e.g. if your default branch name is not master, use type=raw with a boolean expression:

tags: |
  # set latest tag for master branch
  type=raw,value=latest,enable=${{ github.ref == format('refs/heads/{0}', 'master') }}  

You can also use the {{is_default_branch}} global expression to conditionally tag with latest for the default branch:

tags: |
  # set latest tag for default branch
  type=raw,value=latest,enable={{is_default_branch}}  

priority attribute

priority=<int> attribute is used to sort tags in the final list. The higher the value, the higher the priority. The first tag in the list (higher priority) will be used as the image version for generated OCI label and version output. Each tags type attribute has a default priority:

Attribute	Default priority
schedule	1000
semver	900
pep440	900
match	800
edge	700
ref	600
raw	200
sha	100

Global expressions

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

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}}  

{{branch}}

Returns the branch name that triggered the workflow run. Will be empty if not a branch reference:

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

{{tag}}

Returns the tag name that triggered the workflow run. Will be empty if not a tag reference:

Event	Ref	Output
pull_request	refs/pull/2/merge
push	refs/heads/master
push	refs/heads/my/branch
push tag	refs/tags/v1.2.3	v1.2.3

{{sha}}

Returns the short commit SHA that triggered the workflow run (e.g., 90dd603).

{{base_ref}}

Returns the base ref or target branch of the pull request that triggered the workflow run. Will be empty for a branch reference:

Event	Ref	Output
pull_request	refs/pull/2/merge	master
push	refs/heads/master
push	refs/heads/my/branch
push tag*	refs/tags/v1.2.3	master

*base_ref is available in the push payload but doesn't always seem to return the expected branch when the push tag event occurs. It's also not documented in GitHub docs. We keep it for backward compatibility, but it's not recommended relying on it. More context in #192.

{{is_default_branch}}

Returns true if the branch that triggered the workflow run is the default one, otherwise false.

{{date '<format>' tz='<timezone>'}}

Returns the current date rendered by its moment format. Default tz is UTC.

Expression	Output example
{{date 'YYYYMMDD'}}	20200110
{{date 'dddd, MMMM Do YYYY, h:mm:ss a'}}	Friday, January 10th 2020, 3:25:50 pm
{{date 'YYYYMMDD-HHmmss' tz='Asia/Tokyo'}}	20200110-093000

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.') }}  

JSON output object

The json output is a JSON object composed of the generated tags and labels so that you can reuse them further in your workflow using the fromJSON function:

      -
        name: Docker meta
        uses: docker/metadata-action@v4
        id: meta
        with:
          images: name/app
      -
        name: Build and push
        uses: docker/build-push-action@v4
        with:
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          build-args: |
            BUILDTIME=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.created'] }}
            VERSION=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.version'] }}
            REVISION=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.revision'] }}            

Overwrite labels

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

      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v4
        with:
          images: name/app
          labels: |
            maintainer=CrazyMax
            org.opencontainers.image.title=MyCustomTitle
            org.opencontainers.image.description=Another description
            org.opencontainers.image.vendor=MyCompany            

Contributing

Want to contribute? Awesome! You can find information about contributing to this project in the CONTRIBUTING.md