Learning Notes #01 - Github Actions

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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 Workflowon: pushjobs:  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 Workflowon: pushjobs:  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 Workflowon:  push:    branches:      - mainjobs:  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 Workflowon:  push:    branches:      - mainjobs:  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 }}"

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