GitHub Actions Fundamentals for Beginners

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1. What is GitHub Actions?

GitHub Actions is an automated CI/CD (Continuous Integration and Continuous Delivery) platform built directly into GitHub. It allows you to automate software workflows directly from your repository—such as building code, running tests, publishing packages, or deploying applications—whenever specific GitHub events occur.

YAML

# Simple example: Running tests whenever code is pushed
name: CI Pipeline
on: [push]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm install
      - run: npm test

2. What is a Workflow?

A Workflow is an automated, configurable process defined in a .yml (or .yaml) file stored inside your repository’s .github/workflows/ directory. A repository can have multiple workflows (e.g., one for unit testing, one for code linting, and one for production deployments).

Workflows are triggered by events (like a push, pull_request, or schedule) and consist of one or more jobs.

YAML

# .github/workflows/greeting.yml
name: Daily Greeting
on:
  schedule:
    - cron: '0 9 * * 1-5' # Runs every weekday at 9 AM UTC

jobs:
  greet:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Good morning, team!"

3. What is a Runner?

A Runner is an application or server that executes the jobs inside a GitHub Actions workflow. When a workflow is triggered, GitHub assigns a runner to listen for available jobs, run the steps, and stream the logs and results back to GitHub.

Runners come pre-installed with standard development tooling (Git, Node.js, Python, Docker, Docker Compose, CLI tools, etc.).

4. Difference Between Job and Step

  • Job: A group of steps that execute on the same runner instance. By default, if a workflow has multiple jobs, they run in parallel unless configured to run sequentially using needs.
  • Step: An individual task within a job. Steps run sequentially on the runner and share the same environment and filesystem. A step can either run a shell command (run) or execute a reusable action (uses).
FeatureJobStep
ExecutionRuns in parallel (default) or sequentiallyAlways runs sequentially inside its parent job
EnvironmentRuns on its own separate virtual machine / runnerShares the virtual machine environment with other steps in the job
Data SharingFilesystem is isolated from other jobsShares local filesystem changes directly with subsequent steps

YAML

jobs:
  build_job: # JOB 1
    runs-on: ubuntu-latest
    steps:
      - name: Step 1 # STEP 1.1
        run: echo "Compiling code..."
      - name: Step 2 # STEP 1.2
        run: echo "Creating build artifact..."

  deploy_job: # JOB 2 (Depends on JOB 1)
    needs: build_job
    runs-on: ubuntu-latest
    steps:
      - name: Step 1 # STEP 2.1
        run: echo "Deploying build..."

5. What is YAML?

YAML (“YAML Ain’t Markup Language”) is a human-readable data format used for configuration files. GitHub Actions uses YAML to structure workflows. It relies strictly on indentation (spaces, never tabs) and key-value pairs to establish hierarchy.

YAML

# Basic YAML structure rules:
string_key: "value"
number_key: 100
boolean_key: true

list_example:
  - item1
  - item2

nested_object:
  parent:
    child: "value"

6. What are GitHub-Hosted Runners?

GitHub-hosted runners are fully managed virtual machines hosted by GitHub. Every time a job runs, GitHub spins up a fresh, ephemeral VM running your choice of operating system (Ubuntu Linux, Windows, or macOS), runs the job, and destroys the VM afterward.

  • Pros: Zero maintenance, completely clean environment per run, automatically updated software packages.
  • Syntax: runs-on: ubuntu-latest, runs-on: windows-latest, or runs-on: macos-latest.

YAML

jobs:
  check-os:
    runs-on: macos-latest
    steps:
      - run: sw_vers # Checks macOS version

7. What are Self-Hosted Runners?

Self-hosted runners are machines (physical servers, local VMs, cloud instances on AWS/Azure, or Docker containers) that you set up and manage yourself, then register with GitHub.

  • Pros: Access to private internal networks/databases, custom hardware requirements (e.g., GPUs for AI/ML training), faster builds through persistent caching.
  • Cons: You are responsible for OS updates, security, and scaling.
  • Syntax: runs-on: self-hosted.

YAML

jobs:
  internal-deploy:
    runs-on: self-hosted
    steps:
      - run: ./deploy-to-private-datacenter.sh

8. What are GitHub Secrets?

GitHub Secrets are encrypted environment variables stored securely in repository, organization, or environment settings. They allow you to store sensitive credentials (e.g., API keys, database passwords, deployment tokens) without hardcoding them into your source code.

GitHub automatically masks secrets in workflow logs (replacing secret values with ***).

YAML

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - name: Login to Docker Hub
        run: docker login -u ${{ secrets.DOCKER_USERNAME }} -p ${{ secrets.DOCKER_PASSWORD }}

9. What is workflow_dispatch?

workflow_dispatch is an event trigger that allows you to run a workflow manually. Once added to on:, a “Run workflow” button appears in the GitHub Actions tab UI. It can also accept custom input parameters (text, drop-downs, booleans).

YAML

name: Manual Release
on:
  workflow_dispatch:
    inputs:
      environment:
        description: 'Target deployment environment'
        required: true
        default: 'staging'
        type: choice
        options:
          - staging
          - production

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Deploying to ${{ inputs.environment }}"

10. What is actions/checkout?

actions/checkout is an official, reusable action (actions/checkout@v4) provided by GitHub.

When a job starts, the runner’s workspace is completely empty. actions/checkout clones your repository’s code into the workspace so that subsequent steps (like linter checks, test runs, or build tools) can access and execute against your project files.

YAML

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      # Without checkout, npm build will fail because package.json is missing
      - name: Download repository code
        uses: actions/checkout@v4

      - name: Build project
        run: npm run build

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