5. GitLab CI/CD Basics

Continuous Integration (CI) and Continuous Delivery (CD) are the core pillars of modern DevOps. GitLab includes an industry-leading, native CI/CD system. There are no plugins to install, no third-party servers to configure—just add a configuration file to your repository and push!

The Heart of the Pipeline: `.gitlab-ci.yml`

To activate GitLab CI/CD, you place a special file named .gitlab-ci.yml in the root directory of your project. This file is written in YAML syntax and defines the exact structure, order, and instructions of your pipeline.

Key Structural Concepts

• Jobs: The smallest executable unit. A job defines *what* should be done (e.g. run a test suite, compile an application).
• Stages: Groups of jobs that execute in sequential order. Standard stages are: `build`, `test`, and `deploy`.
• Pipelines: The overall collection of jobs split across different stages. If any job in a stage fails, the pipeline halts (by default) and subsequent stages will not execute.

A Complete Example of a `.gitlab-ci.yml` File

Below is a professional, annotated GitLab CI/CD configuration file for a Node.js/React application:

# Define the default Docker image to run the jobs inside
default:
  image: node:18-alpine

# Define the sequence of stages
stages:
  - install
  - test
  - build
  - deploy

# Job 1: Install dependencies and save to cache
install_dependencies:
  stage: install
  script:
    - npm ci
  cache:
    key:
      files:
        - package-lock.json
    paths:
      - node_modules/

# Job 2: Run Unit Tests
run_unit_tests:
  stage: test
  script:
    - npm test

# Job 3: Build application and save build folder as an artifact
build_app:
  stage: build
  script:
    - npm run build
  artifacts:
    paths:
      - build/
    expire_in: 1 week

# Job 4: Deploy to staging (executed only on the 'main' branch)
deploy_to_staging:
  stage: deploy
  script:
    - echo "Deploying build artifacts to staging server..."
  rules:
    - if: $CI_COMMIT_BRANCH == "main"

Understanding Artifacts vs. Cache

It is easy to confuse these two critical concepts: