CI/CD Overview

Continuous Integration (CI) and Continuous Deployment (CD) are practices in modern software development that automate the process of building, testing, and deploying applications. They aim to reduce manual effort, increase reliability, and ensure that new features or bug fixes reach production quickly.

Key Concepts

• Continuous Integration (CI)
  Developers frequently merge code changes into a shared repository. Automated builds and tests are triggered to catch issues early.

• Continuous Deployment (CD)
  After passing CI checks, changes are automatically deployed to production or staging environments, reducing human error.

• Stages
  CI/CD pipelines are divided into stages such as build, test, and deploy. Each stage can contain multiple steps or jobs.

• Automation Tools
  Common CI/CD tools include GitLab CI, GitHub Actions, Jenkins, and CircleCI.

Example: GitLab CI/CD Pipeline

Below is a simple GitLab CI/CD configuration that deploys a project called n-docs using Docker Compose.

stages:
  - deploy

deploy:
  stage: deploy
  script:
    - |
      if [ ! -d "/home/gitlab-runner/n-docs/.git" ]; then
        git clone https://gitlab.j551n.com/j551n/n-docs.git /home/gitlab-runner/n-docs
      else
        cd /home/gitlab-runner/n-docs
        git fetch origin
        git reset --hard origin/main
      fi
    - cd /home/gitlab-runner/n-docs
    - docker compose stop n-docs || true
    - docker compose up --build -d
  only:
    - main
    - shared

How This Works

1. Check out the repository
   The pipeline first verifies if the repository exists on the runner. If it doesn't, it clones it. Otherwise, it fetches the latest changes and performs a hard reset to match the remote branch exactly.

2. Navigate to project folder
   The script ensures all subsequent commands run in the correct directory.

3. Stop existing services
   The Docker service n-docs is stopped if it's already running. The || true ensures the pipeline doesn't fail if the service is not running.

4. Deploy with Docker Compose
   The service is rebuilt and started in detached mode.

5. Trigger conditions
   This job runs only for commits to the main and shared branches.

Benefits

• Automates deployment, reducing manual errors.
• Ensures the application is always up-to-date with the latest changes.
• Provides a repeatable and reliable deployment process.

Further Reading

• GitLab CI/CD Documentation
• Docker Compose