Container Prebuilt Action Template

Use this template to bootstrap the creation of a container action. 🚀

This template includes compilation support, tests, a validation workflow, publishing, and versioning guidance. The core difference between this template and actions/container-action is that this template does not build the container image on every action run. Instead, the action pulls the image from GitHub Container Registry (ghcr.io).

If you would like to use the GitHub Actions Toolkit in your container action, see the Container Toolkit Action repository.

Create Your Own Action

To create your own action, you can use this repository as a template! Just follow the below instructions:

1. Click the Use this template button at the top of the repository
2. Select Create a new repository
3. Select an owner and name for your new repository
4. Click Create repository
5. Clone your new repository

Important

Make sure to remove or update the CODEOWNERS file! For details on how to use this file, see About code owners.

Initial Setup

After you've cloned the repository to your local machine or codespace, you'll need to perform some initial setup steps before you can develop your action.

Note

You'll need to have a reasonably modern version of Docker handy (e.g. docker engine version 20 or later).

1. 🛠️ Build the container

   Make sure to replace actions/container-prebuilt-action with an appropriate label for your container.

   docker build -t actions/container-prebuilt-action .

2. ✅ Test the container

   You can pass individual environment variables using the --env or -e flag.

   $ docker run --env INPUT_WHO_TO_GREET="Mona Lisa Octocat" actions/container-prebuilt-action
   ::notice file=entrypoint.sh,line=7::Hello, Mona Lisa Octocat!

   Or you can pass a file with environment variables using --env-file.

   $ cat ./.env.test
   INPUT_WHO_TO_GREET="Mona Lisa Octocat"
   
   $ docker run --env-file ./.env.test actions/container-prebuilt-action
   ::notice file=entrypoint.sh,line=7::Hello, Mona Lisa Octocat!

Update the Action Metadata

The action.yml file defines metadata about your action, such as input(s) and output(s). For details about this file, see Metadata syntax for GitHub Actions.

When you copy this repository, update action.yml with the name, description, inputs, and outputs for your action.

Important

Make sure to update the image property to use your repository!

runs:
  using: docker
  image: docker://ghcr.io/<owner>/<repository>:<tag>

Update the Action Code

In this template, the container action runs a shell script, entrypoint.sh, when the container is launched. Since you can choose any base Docker image and language you like, you can change this to suite your needs. There are a few main things to remember when writing code for container actions:

• Inputs are accessed using argument identifiers or environment variables (depending on what you set in your action.yml). For example, the first input to this action, who-to-greet, can be accessed in the entrypoint script using the $INPUT_WHO_TO_GREET environment variable.

  GREETING="Hello, $INPUT_WHO_TO_GREET!"

• GitHub Actions supports a number of different workflow commands such as creating outputs, setting environment variables, and more. These are accomplished by writing to different GITHUB_* environment variables. For more information, see Workflow commands.

  Scenario	Example
  Set environment vars	echo "MY_VAR=my-value" >> "$GITHUB_ENV"
  Set outputs	echo "greeting=$GREETING" >> "$GITHUB_OUTPUT"
  Prepend to PATH	echo "$HOME/.local/bin" >> "$GITHUB_PATH"
  Set pre/post vars	echo "MY_VAR=my-value" >> "$GITHUB_STATE"
  Set step summary	echo "{markdown}" >> "$GITHUB_STEP_SUMMARY"

  You can write multiline strings using the following syntax:

  {
    echo "JSON_RESPONSE<<EOF"
    curl https://example.com
    echo "EOF"
  } >> "$GITHUB_ENV"

• Make sure that the script being run is executable!

  git add entrypoint.sh
  git update-index --chmod=+x entrypoint.sh

So, what are you waiting for? Go ahead and start customizing your action!

1. Create a new branch

   git checkout -b releases/v1

2. Replace the contents of entrypoint.sh with your action code

3. Build and test the container

   docker build -t actions/container-prebuilt-action .
   docker run actions/container-prebuilt-action "Mona Lisa Octocat"

4. Commit your changes

   git add .
   git commit -m "My first action is ready!"

5. Push them to your repository

   git push -u origin releases/v1

6. Create a pull request and get feedback on your action

7. Merge the pull request into the main branch

Your action is now published! 🚀

For information about versioning your action, see Versioning in the GitHub Actions toolkit.

Releasing Versions

By default, the cd.yml workflow in this repository is configured to release a new version of the action any time a pull request is merged into the default branch (main). In order to prevent existing versions from being overwritten, the version-check.yml workflow can be used as a required status check in your branch protection rules.

As part of the pull request, make sure to update the .version file to a new Semantic Version.

Usage

After testing, you can create version tag(s) that developers can use to reference different stable versions of your action. For more information, see Versioning in the GitHub Actions toolkit.

To include the action in a workflow in another repository, you can use the uses syntax with the @ symbol to reference a specific branch, tag, or commit hash.

steps:
  - name: Checkout
    id: checkout
    uses: actions/checkout@v3

  - name: Test Local Action
    id: test-action
    uses: actions/container-prebuilt-action@v1 # Commit with the `v1` tag
    with:
      who-to-greet: Mona Lisa Octocat

  - name: Print Output
    id: output
    run: echo "${{ steps.test-action.outputs.greeting }}"