GitLab CI CD Core Components

In this guide, we’ll dive into the four essential GitLab CI/CD building blocks—Pipeline, Stages, Jobs, and Scripts—and show you how they collaborate to automate testing, building, and deployment. By the end, you’ll have a clear understanding of how to configure a robust .gitlab-ci.yml and choose the right pipeline type for your workflow.

CI/CD Core Components Overview

Pipeline

A pipeline is defined via a .gitlab-ci.yml file at the root of your repo and represents the blueprint for your CI/CD workflow.

Key points:

• Definition: YAML file named .gitlab-ci.yml.
• Naming: Use workflow:name to assign a custom name shown in the Pipelines tab.
• Triggers: Pipelines start on push, merge_request, schedule, or manual actions.
• Conditions: Use rules to control when pipelines run.

Example: Run pipeline only on commits to main

workflow:
  name: My Awesome App Pipeline
  rules:
    - if: $CI_COMMIT_BRANCH == 'main'

Jobs

A job is the fundamental execution unit in a pipeline:

• Execution: Runs on a GitLab Runner (shared or self-hosted).
• Runner selection: Use tags to pick specific runners.
• Stage assignment: Each job belongs to a defined stage.

Example: Selecting a specific runner

unit_test_job:
  stage: test
  tags:
    - saas-linux-small-amd64

Scripts

The script section lists shell commands executed by the job:

• Sequential execution: Commands run in order.
• Common use cases: Install dependencies, build code, run tests, deploy artifacts, perform security scans.
• Before/after hooks:
  • before_script: Setup steps (e.g., install Node.js, configure DB).
  • after_script: Cleanup tasks (e.g., remove temp files).

before_script:
  - echo "Setting up environment"
script:
  - npm install
  - npm test
after_script:
  - echo "Cleaning up"

Example .gitlab-ci.yml

Here’s a complete sample that defines two stages—test and deploy—and a workflow rule:

workflow:
  name: My Awesome App Pipeline
  rules:
    - if: $CI_COMMIT_BRANCH == 'main'

stages:
  - test
  - deploy

unit_test_job:
  stage: test
  tags:
    - saas-linux-small-amd64
  before_script:
    - echo "Install NodeJS"
  script:
    - npm install
    - npm test
  after_script:
    - echo "Tests complete"

deploy_job:
  stage: deploy
  script:
    - echo "Deploying to production..."

In this configuration:

• The pipeline runs only on main.
• The test stage executes unit_test_job with setup, tests, and teardown.
• The deploy stage runs deploy_job after successful tests.

Stages

Stages define the sequence of execution in a pipeline. Jobs within the same stage run in parallel. Common stages include:

Pipeline Types

Choose the pipeline type that best suits your project complexity and team structure:

Links and References

• GitLab CI/CD Documentation
• GitLab CI/CD YAML Reference
• CI/CD Variables in GitLab