Parallel Jobs in GitHub Actions

1. Introduction

In GitHub Actions, parallel jobs allow multiple jobs in a workflow to run simultaneously. This can significantly reduce the time it takes for CI/CD pipelines to complete, especially in large projects with extensive testing and building processes.

2. Key Concepts

What are Jobs?

A job is a set of steps that execute on the same runner. Jobs can run sequentially or in parallel.

What are Runners?

Runners are servers that run your workflows when you trigger them. GitHub provides hosted runners, or you can set up your own self-hosted runners.

Dependencies

Jobs can have dependencies, meaning that certain jobs can be configured to wait for others to complete before they start.

3. Defining Parallel Jobs

Step-by-Step Process

To define parallel jobs in a GitHub Actions workflow, follow these steps:

Open your GitHub repository and navigate to the .github/workflows directory.
Create a new YAML file (e.g., ci.yml) for your workflow.
Define the jobs section in the workflow file.
Specify multiple jobs without any dependencies to allow them to run in parallel.

Example Workflow with Parallel Jobs

name: CI

on: [push, pull_request]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v2
      - name: Build
        run: echo "Building the project..."

  test:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v2
      - name: Run tests
        run: echo "Running tests..."

  deploy:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v2
      - name: Deploy
        run: echo "Deploying application..."

In this example, build, test, and deploy jobs can run in parallel since they do not have any dependencies defined.

4. Best Practices

Ensure that jobs are independent to maximize the benefits of parallel execution.
Use caching to speed up your jobs, especially for dependencies and build artifacts.
Monitor job logs to troubleshoot issues efficiently.
Use matrix builds to run tests across multiple environments in parallel.

5. FAQ

Can I run jobs sequentially?

Yes, you can run jobs sequentially by using the needs keyword to define dependencies between jobs.

How many jobs can run in parallel?

The number of concurrent jobs depends on your GitHub plan. Free accounts have a limit of 20 concurrent jobs, while paid plans have higher limits.

Can parallel jobs share data?

Parallel jobs cannot share data directly. You can use artifacts to pass data between jobs if necessary.