sajibsrs / notes-on-github-actions

Brief notes on GitHub Actions.

Notes on GitHub Actions

GitHub actions is an implementation of a cohesive automated continuous integration, continuous delivery (CI/CD) workflow.

# Contents

• 1 # Workflows
• 2 # Events
• 3 # Jobs
• 4 # Steps
• 5 # Actions
• 6 # Runners
• License

1 # Workflows

A workflow is a configurable automated process that that runs a single or multiple jobs. Workflows are defined in a YAML file. GitHub checks the repository for workflow configuration file and runs when triggered by an event in the repository. Workflows can also be triggered manually or on a predefined schedule.

One repository can have multiple workflows for different operations. Such as, a repository can have one workflow to build and test pull requests and another to deploy application every time a release is created.

Note: Workflows can be reused rather than duplicating existing one.

• Reusing workflow [ext]
• Learn about workflow [ext]

Note: [ext] in a link denotes, an external link that leads to other location outside of this document.

2 # Events

An event is a specific activity in a repository that triggers a workflow run. For example, activity can originate from GitHub on creating pull request, opening issue, push, or committing to a repository. Workflow run can be triggered in three ways:

1. Schedule
2. Posting to a REST API
3. Manually

GitHub events [ext]

3 # Jobs

A job is a set of steps that run on the same runner. Multiple jobs within the same workflow can run sequentially, although by default they runs in parallel.

jobs:
  tests_manual_workflow:
    runs-on: ubuntu-latest

4 # Steps

Steps are individual tasks that runs commands, such as a shell command or an action, in a job within a workflow. Steps can share data among themselves as they runs on the same runner.

steps:
  - run: >
    echo "User ${{ github.event.inputs.username }} ran a workflow."
    echo "Reason ${{ github.event.inputs.reason }}."

5 # Actions

Actions are standalone commands. They combined into steps to create job. User can create their own actions and share with the community. User can also use actions that have already been created by the community.

There are three different types of actions:

1. Docker container
2. Javascript
3. Composite

jobs:
  stale:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/stale@v3

6 # Runners

A runner is a server application, often installed on a virtual machine or docker container. It runs a job from GitHub Actions workflow. A runner has one job at a time and provides feedback to GitHub. In a runner, steps executes in the same instance of the virtual machine (VM). This allows the actions within that job to share information using the filesystem.

There are two types of runners:

1. GitHub-hosted runners
2. Self-hosted runners

Note: GitHub supports Windows, macOS, and Linux operating systems for runners.

jobs:
  build:
    runs-on: macos-latest

GitHub hosted runner is managed by GitHub. On the other hand, self-hosted runners are created and managed by users.

Note: There are three types of actions: Docker container actions, JavaScript actions, and composite run steps actions.

# License

MIT