2. GitLab Architecture & Self-Hosting

One of GitLab’s greatest strengths is its architectural flexibility. Unlike platforms that are strictly SaaS, GitLab is designed from the ground up to be deployed on-premise, inside custom private clouds, or on managed container platforms like Kubernetes.

GitLab Deployment Models

You can consume and host GitLab in three main ways:

• GitLab SaaS (GitLab.com): Managed entirely by GitLab. You create an account, create groups, and start coding immediately. No installation or infrastructure maintenance required.
• GitLab Self-Managed (Omnibus): Installed on a single virtual machine or server (typically Ubuntu, CentOS, or Debian). This uses GitLab's "Omnibus" package, which contains all components pre-configured.
• GitLab Cloud-Native (Kubernetes / Helm): Designed to run on a container orchestrator. It scales horizontally, separating stateless workloads from stateful data stores.

Under the Hood: Inside the GitLab Monolith

Although it appears to users as a single dashboard, GitLab's backend is a highly optimized set of microservices centered around a Ruby on Rails application:

• Workhorse: A reverse-proxy daemon written in Go that handles heavy HTTP requests (such as git push/pull, file transfers, and ZIP downloads) to free up Rails threads.
• Puma: The web server running the core Ruby on Rails web framework.
• Gitaly: A Git RPC service written in Go. Instead of having the Rails app read local Git disk paths directly, Gitaly provides high-performance access to repositories stored on disk.
• Sidekiq: A background job controller that processes asynchronous work like sending emails, processing webhooks, and trigger pipelines.
• PostgreSQL: The primary relational database holding project settings, user accounts, merge requests, issues, and pipelines.
• Redis: An in-memory cache and key-value store for caching sessions, background queues, and real-time page updates.

Setting Up GitLab Locally with Docker

The easiest way to test GitLab's self-managed environment is by spinning up the official Docker container. Below is a standard `docker-compose.yml` to launch GitLab locally:

version: '3.6'
services:
  web:
    image: 'gitlab/gitlab-ce:latest'
    restart: always
    hostname: 'localhost'
    environment:
      GITLAB_OMNIBUS_CONFIG: |
        external_url 'http://localhost:8989'
        # Add any custom configuration here
    ports:
      - '8989:8989'
      - '2222:22'
    volumes:
      - './config:/etc/gitlab'
      - './logs:/var/log/gitlab'
      - './data:/var/opt/gitlab'
    shm_size: '256m'

To run this docker setup, simply run:

docker-compose up -d

Once started, you can access your local GitLab instance at `http://localhost:8989`. The default username is `root`, and the initial password can be retrieved from `./config/initial_root_password` inside the container host directories.