GitLab CICD Architecture SaaS

In this guide, we’ll dive into how GitLab CI/CD pipelines leverage Runners and Executors in both SaaS and self-managed environments. You’ll learn deployment options, core components, and the end-to-end workflow powering your automated builds and deployments.

GitLab Server Overview

GitLab Server is an open-source DevOps platform that centralizes the entire software development lifecycle:

• Git repository management with fine-grained access controls
• Issue tracking and project planning
• Built-in CI/CD pipelines for automated testing and deployment
• Container & package registries for Docker, Helm, npm, and more
• Security & compliance scanning, auditing, and reporting

GitLab is available as:

• GitLab SaaS (hosted by GitLab.com)
• GitLab Self-Managed (on your infrastructure)

Both share the same core features but differ in control, customization, and operational responsibilities.

SaaS vs Self-Managed: A Side-by-Side Comparison

Choosing the right deployment model is critical for scaling, security, and cost management:

GitLab SaaS

Key Benefits

• Zero infrastructure overhead: No servers to install or maintain.
• Quick setup: Start CI/CD in minutes, even without DevOps expertise.
• Elastic scalability: Automatic scaling and pay-as-you-go pricing.
• High availability: SLA-backed uptime and redundancy managed by GitLab.com.
• Automatic updates: Always on the latest version with security patches.
• Built-in security: Vulnerability scanning, dependency checks, and DAST/SAST as a service.

Considerations

• Limited platform customization and plugin support.
• Data residency and privacy depend on GitLab.com’s infrastructure.
• Potential cost growth for large teams or high-load pipelines.

GitLab Self-Managed

Key Benefits

• Full control & customization: Configure runners, storage, and plugins as needed.
• Complete data ownership: Host code, metadata, and artifacts on your hardware.
• No vendor lock-in: Freedom to migrate between clouds or on-premises.
• Cost efficiency at scale: More predictable costs for large enterprises.

Considerations

• Requires in-house expertise for installation, upgrades, and security.
• Infrastructure must be provisioned and scaled by your team.
• You are responsible for patching, backup, and disaster recovery.

GitLab CI/CD Workflow Architecture

The following diagram shows how the GitLab Server, Runner, and Executor collaborate to process a CI/CD job:

Workflow Phases

1. Registration Phase

1. Runner sends a POST to /runners/register with the registration token.
2. GitLab Server validates and returns a runner token.
3. Runner stores this token for all future interactions.

2. Job Request Phase

1. Registered Runner polls /jobs/request, authenticated with its runner token.
2. Server responds with a job payload containing a job token for that execution.

3. Job Execution Phase

1. Runner passes the payload to the Executor.
2. Executor uses the job token to:
   • Clone the repository
   • Download dependencies and artifacts
   • Execute the CI/CD script in an isolated environment (Docker, VM, shell)
3. Isolation prevents cross-job interference and secures the runner host.

4. Job Reporting Phase

1. Executor gathers logs, artifacts, and exit status.
2. It POSTs back to /jobs/:id/trace using the job token.
3. GitLab Server records results and updates the pipeline UI.

Token Exchange Summary

By understanding these components—Server, Runner, Executor—and their interactions, you can design scalable, secure CI/CD pipelines on either GitLab SaaS or Self-Managed. Optimize runner tagging, parallelism, and caching to accelerate builds and reduce costs.

Links and References

• GitLab Runner Documentation
• Installing GitLab Self-Managed
• GitLab CI/CD Pipelines
• GitLab Security Features