Docker Actions in GitHub Actions

1. Introduction

Docker Actions allow you to create reusable workflows that can be packaged and shared across GitHub repositories. This lesson covers the essential concepts, steps to create Docker Actions, and best practices for using them effectively.

2. What are Docker Actions?

Docker Actions are custom actions that run within a Docker container. They are defined in a Dockerfile and can be used in GitHub workflows to automate tasks.

Key Definitions

• Action: A custom application for performing a task in a workflow.
• Dockerfile: A file that contains instructions on how to build a Docker image.
• Workflow: A set of instructions that define the automation process in GitHub Actions.

3. Creating Docker Actions

To create a Docker Action, follow these steps:

1. Create a new directory for your action.
2. Create a Dockerfile with the necessary instructions.
3. Create an action.yml file to define the action.
4. Build and test your Docker image.
5. Publish your action to the GitHub Marketplace.

Example Dockerfile

FROM node:14

WORKDIR /usr/src/app

COPY package*.json ./
RUN npm install

COPY . .

CMD ["node", "index.js"]
        

Example action.yml

name: 'My Docker Action'
description: 'A simple action that runs a Node.js app'
inputs:
  my_input:
    description: 'An example input'
    required: true
runs:
  using: 'docker'
  image: 'Dockerfile'
  args:
    - ${{ inputs.my_input }}
        

4. Best Practices

When creating Docker actions, consider the following best practices:

• Keep your Docker images small by using multi-stage builds.
• Use environment variables for configuration.
• Document your action with clear descriptions and examples.
• Version your actions carefully to avoid breaking changes.

5. FAQ