How to deploy on GitLab?

Deployment in GitLab CI/CD is performed by configuring the .gitlab-ci.yml file in the root directory of the project. This file defines pipelines, stages, and jobs.

The typical deployment process includes:

• Build: Creating artifacts (Docker images, executable files, etc.).
• Testing: Running Unit, Integration, and End-to-End tests.
• Deploy: Deploying artifacts to target environments.

Example of .gitlab-ci.yml for deploying a Docker image:

stages:
  - build
  - deploy

build:
  stage: build
  image: docker:latest
  services:
    - docker:dind
  script:
    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
    - docker build -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA" .
    - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA"

deploy_staging:
  stage: deploy
  image: registry.gitlab.com/gitlab-org/cloud-native/gitlab-agent/agentk/kubectl:latest # Using kubectl
  script:
    - kubectl config use-context my-kubernetes-context # Switching to the required context
    - kubectl apply -f kubernetes/deployment-staging.yaml # Deploy YAML file
  environment:
    name: staging
  only:
    - main # Run job only on commits to the main branch

deploy_production:
  stage: deploy
  image: registry.gitlab.com/gitlab-org/cloud-native/gitlab-agent/agentk/kubectl:latest
  script:
    - kubectl config use-context my-kubernetes-context
    - kubectl apply -f kubernetes/deployment-production.yaml
  environment:
    name: production
  when: manual # Manual job trigger
  only:
    - main

Key concepts:

• Stages: Define the sequence of job execution.
• Jobs: Specific tasks executed in stages. Can use different Docker images.
• Runners: Agents that execute jobs. Can be shared, specific, or group runners.
• Variables: Used to store sensitive data or configuration. Can be predefined or user-defined (in CI/CD settings).
• Environments: Link deployments to specific environments (staging, production). Facilitate version tracking and rollbacks.
• Rules/Only/Except: Define when a job should run.

Tools for deploying to various platforms include:

Platform	Tool	Example usage in .gitlab-ci.yml
Kubernetes	kubectl, Helm	Using images with kubectl or Helm
Docker Swarm	docker	Using docker image
Cloud Platforms (AWS, GCP, Azure)	AWS CLI, gcloud, az	Using images with respective CLI tools
SSH	ssh	Using ssh image and executing commands

Deployment optimization includes:

• Caching: Speeds up build.
• Parallel job execution: Reduces pipeline time.
• Blue/Green or Canary deployment: To reduce risks.

Sensitive data (passwords, API keys) should be stored in masked CI/CD variables.