Design Google-scale CI/CD pipeline

You are asked to design a Continuous Integration / Continuous Deployment (CI/CD) platform and pipeline that can support a very large engineering organization, similar in scale to a company like Google.

The system should support tens of thousands of developers, millions of lines of code, and large numbers of builds and deployments per day.

Requirements

Clarify and then design for the following (you may make reasonable assumptions, but state them clearly):

Functional Requirements

• Source control integration
  • Integrate with a version control system (e.g., Git) hosting thousands of repositories or a large monorepo.
  • Trigger CI pipelines on events such as:
    • Pull request creation/update
    • Commits to main or release branches
    • Scheduled (nightly) builds
• Build and test pipeline
  • Automatically build code and run unit, integration, and end-to-end tests.
  • Support many programming languages and build tools.
  • Support configurable pipelines per service/repository.
• Artifact management
  • Store build artifacts (e.g., binaries, Docker images, archives) in a reliable, versioned artifact repository.
  • Allow fast retrieval and reuse of artifacts.
• Deployment
  • Support automated deployments to multiple environments (dev, staging, prod).
  • Support safe deployment strategies (e.g., canary, rolling updates, blue-green).
  • Support automated rollback on failure.
• User experience
  • Developers should be able to:
    • See build/test/deploy status and logs.
    • Re-trigger or cancel runs.
    • Configure pipelines via configuration files or a UI.

Non-Functional Requirements

• Scale
  • Assume roughly:
    • 30,000+ developers.
    • 100,000+ commits per day.
    • Up to 1,000,000 pipeline jobs per day (builds/tests/deployments).
  • The system should be horizontally scalable.
• Performance
  • Median feedback time (from commit/pull request to CI result) should be within a few minutes.
• Reliability
  • High availability (e.g., 99.9%+ uptime for core control-plane services).
  • No single point of failure.
• Security & Compliance
  • Access control by project/team.
  • Secure handling of secrets (API keys, credentials).
  • Audit logging of who deployed what, when, and where.

What to Design and Discuss

Design the CI/CD system with the above requirements in mind and discuss:

1. High-level architecture
   • Major components/services and how they interact:
     • Event/trigger service
     • Pipeline orchestrator/scheduler
     • Build/test execution workers
     • Artifact storage and container registry
     • Deployment service
     • Configuration store
     • Monitoring and logging
2. Data and control flow
   • Walk through the lifecycle:
     • A developer pushes code or opens a pull request.
     • How the event is captured.
     • How a pipeline is selected and executed.
     • How artifacts are created and stored.
     • How deployments are triggered and monitored.
3. Scalability strategies
   • How you would scale to millions of jobs per day:
     • Job queues and sharded schedulers.
     • Distributed worker pools (e.g., Kubernetes clusters, auto-scaling VMs).
     • Caching and incremental builds (e.g., remote build cache).
     • Parallel and selective test execution.
4. Reliability and fault tolerance
   • Handling:
     • Worker failures
     • Partial region outages
     • Retry policies for flaky jobs
   • Ensuring that a failure in one team’s pipeline does not affect others (multi-tenancy isolation).
5. Security and governance
   • Secret management for deployments.
   • Role-based access control (RBAC) for who can trigger deployments to which environments.
   • Audit logging and compliance reporting.
6. Developer experience
   • How developers define pipelines (e.g., YAML files in repo vs centralized UI).
   • How to make pipelines debuggable (logs, metrics, distributed tracing).
   • Approaches to keep configuration manageable at large scale.

You do not need to provide exact implementation details for every component, but you should propose a clear, coherent architecture, justify major design choices, and explain how your design meets the scale, reliability, and usability requirements.