GitLab CI Cheatsheet

1. Introduction:

GitLab CI/CD is a part of GitLab, a complete DevOps platform, allowing you to define CI/CD pipelines directly within your GitLab repository using the .gitlab-ci.yml file.

2. Key Concepts:

Pipeline: A series of stages that run jobs sequentially or in parallel.
Job: An individual unit of work, such as running tests or deploying code.
Stage: A group of jobs that run in parallel.
Runner: The agent that executes jobs, can be GitLab-hosted or self-hosted.

3. Basic .gitlab-ci.yml Example:

YAML Syntax:

stages:
  - build
  - test
  - deploy

build-job:
  stage: build
  script:
    - echo "Building the project..."
    - make

test-job:
  stage: test


  script:
    - echo "Running tests..."
    - make test

deploy-job:
  stage: deploy
  script:
    - echo "Deploying the project..."
    - make deploy

4. Runners:

Shared Runners: Provided by GitLab and available to all projects.
Specific Runners: Custom runners registered to a specific project or group.
Tags: Use tags to specify which runner should execute a job.

5. Artifacts and Caching:

Artifacts: Save job outputs and make them available to subsequent jobs.
```
artifacts:
  paths:
    - build/
  expire_in: 1 week
```
Caching: Speed up jobs by reusing previously downloaded dependencies.
```
cache:
  paths:
    - node_modules/
```

6. Environments and Deployments:

Environments: Define environments to organize and manage deployments.

deploy-job:
  stage: deploy
  environment:
    name: production
    url: https://myapp.com
  script:
    - echo "Deploying to production..."
    - ./deploy.sh

Manual Deployments: Require manual approval before a job runs.

deploy-job:
  stage: deploy
  script:
    - ./deploy.sh
  when: manual

7. Advanced .gitlab-ci.yml Features:

YAML Anchors: Reuse parts of your YAML configuration.

.default-job: &default-job
  script:
    - echo "Default job script"

job1:
  <<: *default-job

job2:
  <<: *default-job

Includes: Include other YAML files to organize your configuration.
```
include:
  - local: '/templates/.gitlab-ci-template.yml'
```

8. Security and Compliance:

Secret Variables: Store sensitive data securely in GitLab CI/CD.
```
deploy-job:
  script:
    - deploy --token $CI_DEPLOY_TOKEN
```
Protected Branches: Restrict certain jobs to run only on protected branches.

9. Troubleshooting:

Pipeline Logs: Access detailed logs for each job to troubleshoot failures.
Retrying Jobs: Use the GitLab UI to manually retry failed jobs.

10. Best Practices:

Modular Pipelines: Break down your pipeline into stages for better organization.
Use CI/CD Templates: Leverage GitLab’s built-in templates for common CI/CD tasks.
Optimize Runner Usage: Use caching, artifacts, and parallel jobs to reduce pipeline runtime.