Syed Jafer K

GitHub Actions is a CI/CD tool that automates workflows directly from your GitHub repository. I am writing this notes for my future self.

Github: https://github.com/syedjaferk/gh_action_docker_build_push_fastapi_app

0. Github Actions

Github Actions is a managed CI/CD pipeline offering. It provides free runners for running the code.

1. Workflow, Jobs, Steps

A workflow is a collection of jobs defined in a .yml file inside .github/workflows. Each workflow consists of jobs, and jobs have steps.

name: My First Workflow
on: push
jobs:
  example-job:
    runs-on: ubuntu-latest
    steps:
      - name: Print a message
        run: echo "Hello, GitHub Actions!"

2. Availability and Pricing

GitHub Actions is free for public repositories and has free usage limits for private repositories, depending on the plan. Paid plans increase these limits. For detailed pricing, visit the GitHub Actions pricing page.

3. First workflow with basic echo commands

Start with a workflow triggered by any push event. Here’s a simple example,

name: Echo Workflow
on: push
jobs:
  echo-job:
    runs-on: ubuntu-latest
    steps:
      - name: Say Hello
        run: echo "Hello from my first workflow!"

4. Multiline Shell Commands

You can use the | symbol to write multiline shell commands.

name: Push Event Workflow
on:
  push:
    branches:
      - main
jobs:
  push-job:
    runs-on: ubuntu-latest
    steps:
      - name: On Push
        run: echo "Code pushed to main branch!"

5. A new workflow with push events

Workflows can be triggered by specific events like push. This example triggers only on push to the main branch.

name: Push Event Workflow
on:
  push:
    branches:
      - main
jobs:
  push-job:
    runs-on: ubuntu-latest
    steps:
      - name: On Push
        run: echo "Code pushed to main branch!"

6. Using actions in workflow (Marketplace and Open Source)

GitHub Actions Marketplace offers reusable actions. For example, using the actions/checkout action.

steps:
  - name: Checkout Code
    uses: actions/checkout@v3

7. Checkout in code

Checking out your code is essential to access the repository content. Use actions/checkout

steps:
  - name: Checkout Code
    uses: actions/checkout@v3

8. Adding workflow job steps

Each job can have multiple steps.

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Step 1 - Checkout Code
        uses: actions/checkout@v3
      - name: Step 2 - Run a Script
        run: echo "Script running in step 2."

9. Jobs in Parallel and Sequential

To run jobs in parallel, define them without dependencies. For sequential jobs, use needs.

Parallel Jobs:

jobs:
  job1:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Job 1"

  job2:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Job 2"

Sequential Jobs:

jobs:
  job1:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Job 1"

  job2:
    runs-on: ubuntu-latest
    needs: job1
    steps:
      - run: echo "Job 2 after Job 1"

10. Using Multiple Triggers

A workflow can be triggered by multiple events.

on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

11. Expressions and Context Objects

Expressions are used to access variables and contexts like github or env.

steps:
  - name: Use an Expression
    run: echo "Triggered by ${{ github.event_name }}"