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Creating a Custom GitHub Action Using Go

Creating a Custom GitHub Action Using Go

Learn how to create custom GitHub Actions using Dockerfiles and images in Go.

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In this lesson, we will extend our work by turning the tweeter command line into a GitHub Action. This will allow anyone on GitHub building automation to use tweeter to tweet from their own pipeline. Furthermore, we’ll use our tweeter action to tweet when we release new versions of tweeter by extending the release job to use our new action.

In this lesson, we will learn the basics of authoring GitHub Actions. We will create a custom GitHub Action using Go. We will then optimize the start-up time of our custom action by creating a container image.

Basics of custom actions

Custom actions are individual tasks that wrap a collection of related tasks. Custom actions can be executed as individual tasks in workflows and can be shared with the GitHub community.

Types of actions

There are three types of actions: container, JavaScript, and composite actions. Container-based actions use a Dockerfile or a container image reference as the entry point, the starting point of execution for the action, and are useful if we want to author an action in anything but JavaScript or existing actions. Container-based actions offer flexibility in customizing the execution environment of an action, but it comes at the cost of start-up time. If a container-based action depends on a large container image or a slow-building Dockerfile, then the action start-up time will be adversely affected. JavaScript actions can
run directly on the runner machine and are the native expression of an action. JavaScript actions start up quickly and can leverage the GitHub Actions Toolkit, a set of JavaScript packages to make creating actions easier. Composite actions are a collection of steps within a wrapper action. They enable an author to combine a set of disparate steps into a higher-order behavior.

Action metadata

To define an action, we must create an action.yaml file in a GitHub repository. If the action is to be shared publicly, the action.yaml file should be created in the root of the repository. If the action is not to be shared publicly, it is recommended to create the action.yaml file in ./.github/{name-of-action}/action.yaml where {name-of-action} should be substituted with the name of the action. For example, if the tweeter action was only to be used internally, the path of the action metadata would be ./.github/tweeter/action.yaml:

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name: Name of the Action
author: @author
description: Description of your action
branding:
  icon: message-circle
  color: blue
inputs:
  sample:
    description: sample description
    required: true
outputs:
  sampleOutput:
    description: some sample output
runs:
  using: docker
  image: Dockerfile
  args:
  - --sample
  - "${{ inputs.sample }}"

The preceding action.yaml defines the following:

  • The name of the action that will be shown in the GitHub UI.

  • The author of the action.

  • The description of the action.

  • Branding that will be used for the action in the GitHub UI.

  • Input the action will accept.

  • Output the action will return.

  • The runs section, which describes how the action will be executed. ...