Note: GitHub-hosted runners are not currently supported on GitHub Enterprise Server. You can see more information about planned future support on the GitHub public roadmap.
Introduction
In this guide, you'll learn about the basic components needed to create and use a packaged Docker container action. To focus this guide on the components needed to package the action, the functionality of the action's code is minimal. The action prints "Hello World" in the logs or "Hello [who-to-greet]" if you provide a custom name.
Once you complete this project, you should understand how to build your own Docker container action and test it in a workflow.
Self-hosted runners must use a Linux operating system and have Docker installed to run Docker container actions. For more information about the requirements of self-hosted runners, see "About self-hosted runners."
Warning: When creating workflows and actions, you should always consider whether your code might execute untrusted input from possible attackers. Certain contexts should be treated as untrusted input, as an attacker could insert their own malicious content. For more information, see "Security hardening for GitHub Actions."
Prerequisites
You may find it helpful to have a basic understanding of GitHub Actions environment variables and the Docker container filesystem:
Before you begin, you'll need to create a GitHub repository.
-
Create a new repository on your GitHub Enterprise Server instance. You can choose any repository name or use "hello-world-docker-action" like this example. For more information, see "Creating a new repository."
-
Clone your repository to your computer. For more information, see "Cloning a repository."
-
From your terminal, change directories into your new repository.
Shell cd hello-world-docker-action
Creating a Dockerfile
In your new hello-world-docker-action
directory, create a new Dockerfile
file. Make sure that your filename is capitalized correctly (use a capital D
but not a capital f
) if you're having issues. For more information, see "Dockerfile support for GitHub Actions."
Dockerfile
# Container image that runs your code
FROM alpine:3.10
# Copies your code file from your action repository to the filesystem path `/` of the container
COPY entrypoint.sh /entrypoint.sh
# Code file to execute when the docker container starts up (`entrypoint.sh`)
ENTRYPOINT ["/entrypoint.sh"]
Creating an action metadata file
Create a new action.yml
file in the hello-world-docker-action
directory you created above. For more information, see "Metadata syntax for GitHub Actions."
action.yml
# action.yml
name: 'Hello World'
description: 'Greet someone and record the time'
inputs:
who-to-greet: # id of input
description: 'Who to greet'
required: true
default: 'World'
outputs:
time: # id of output
description: 'The time we greeted you'
runs:
using: 'docker'
image: 'Dockerfile'
args:
- ${{ inputs.who-to-greet }}
This metadata defines one who-to-greet
input and one time
output parameter. To pass inputs to the Docker container, you should declare the input using inputs
and pass the input in the args
keyword. Everything you include in args
is passed to the container, but for better discoverability for users of your action, we recommended using inputs.
GitHub will build an image from your Dockerfile
, and run commands in a new container using this image.
Writing the action code
You can choose any base Docker image and, therefore, any language for your action. The following shell script example uses the who-to-greet
input variable to print "Hello [who-to-greet]" in the log file.
Next, the script gets the current time and sets it as an output variable that actions running later in a job can use. In order for GitHub to recognize output variables, you must use a workflow command in a specific syntax: echo "::set-output name=<output name>::<value>"
. For more information, see "Workflow commands for GitHub Actions."
-
Create a new
entrypoint.sh
file in thehello-world-docker-action
directory. -
Add the following code to your
entrypoint.sh
file.entrypoint.sh
Shell #!/bin/sh -l echo "Hello $1" time=$(date) echo "::set-output name=time::$time"
If
entrypoint.sh
executes without any errors, the action's status is set tosuccess
. You can also explicitly set exit codes in your action's code to provide an action's status. For more information, see "Setting exit codes for actions." -
Make your
entrypoint.sh
file executable. Git provides a way to explicitly change the permission mode of a file so that it doesn’t get reset every time there is a clone/fork.Shell $ git add entrypoint.sh $ git update-index --chmod=+x entrypoint.sh
-
Optionally, to check the permission mode of the file in the git index, run the following command.
Shell $ git ls-files --stage entrypoint.sh
An output like
100755 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 0 entrypoint.sh
means the file has the executable permission. In this example,755
denotes the executable permission.
Creating a README
To let people know how to use your action, you can create a README file. A README is most helpful when you plan to share your action publicly, but is also a great way to remind you or your team how to use the action.
In your hello-world-docker-action
directory, create a README.md
file that specifies the following information:
- A detailed description of what the action does.
- Required input and output arguments.
- Optional input and output arguments.
- Secrets the action uses.
- Environment variables the action uses.
- An example of how to use your action in a workflow.
README.md
# Hello world docker action
This action prints "Hello World" or "Hello" + the name of a person to greet to the log.
## Inputs
## `who-to-greet`
**Required** The name of the person to greet. Default `"World"`.
## Outputs
## `time`
The time we greeted you.
## Example usage
uses: actions/hello-world-docker-action@v1
with:
who-to-greet: 'Mona the Octocat'
Commit, tag, and push your action to GitHub Enterprise Server
From your terminal, commit your action.yml
, entrypoint.sh
, Dockerfile
, and README.md
files.
It's best practice to also add a version tag for releases of your action. For more information on versioning your action, see "About custom actions."
git add action.yml entrypoint.sh Dockerfile README.md
git commit -m "My first action is ready"
git tag -a -m "My first action release" v1
git push --follow-tags
Testing out your action in a workflow
Now you're ready to test your action out in a workflow.
- When an action is in a private repository, the action can only be used in workflows in the same repository.
- When an action is in an internal repository, the action can only be used in workflows in the same repository.
- Public actions can be used by workflows in any repository.
Note: GitHub Actions on your GitHub Enterprise Server instance may have limited access to actions on GitHub.com or GitHub Marketplace. For more information, see "Managing access to actions from GitHub.com" and contact your GitHub Enterprise site administrator.
Example using a public action
The following workflow code uses the completed hello world action in the public actions/hello-world-docker-action
repository. Copy the following workflow example code into a .github/workflows/main.yml
file, but replace the actions/hello-world-docker-action
with your repository and action name. You can also replace the who-to-greet
input with your name.
.github/workflows/main.yml
on: [push]
jobs:
hello_world_job:
runs-on: ubuntu-latest
name: A job to say hello
steps:
- name: Hello world action step
id: hello
uses: actions/hello-world-docker-action@v1
with:
who-to-greet: 'Mona the Octocat'
# Use the output from the `hello` step
- name: Get the output time
run: echo "The time was ${{ steps.hello.outputs.time }}"
Example using a private action
Copy the following example workflow code into a .github/workflows/main.yml
file in your action's repository. You can also replace the who-to-greet
input with your name.
.github/workflows/main.yml
on: [push]
jobs:
hello_world_job:
runs-on: ubuntu-latest
name: A job to say hello
steps:
# To use this repository's private action,
# you must check out the repository
- name: Checkout
uses: actions/checkout@v2
- name: Hello world action step
uses: ./ # Uses an action in the root directory
id: hello
with:
who-to-greet: 'Mona the Octocat'
# Use the output from the `hello` step
- name: Get the output time
run: echo "The time was ${{ steps.hello.outputs.time }}"
From your repository, click the Actions tab, and select the latest workflow run. Under Jobs or in the visualization graph, click A job to say hello.
Click Hello world action step, and you should see "Hello Mona the Octocat" or the name you used for the who-to-greet
input printed in the log. Click Get the output time to see the timestamp.