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
Customizing
context input
images input
flavor input
tags input
Notes
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

Files

README.md

Latest commit

History

README.md

File metadata and controls

About

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

`context` input

`images` input

`flavor` input

`tags` input

`type=schedule`

`type=semver`

`type=pep440`

`type=match`

`type=edge`

`type=ref`

`type=raw`

`type=sha`

`priority` attribute

`{{branch}}`

`{{tag}}`

`{{sha}}`

`{{base_ref}}`

`{{is_default_branch}}`

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