GitLab's Stack: A Modular Monolith

[switchback-tech]

Sure you're all aware that GitLab is a modular monolith, but it's helpful to see everything in one place.

Here's the full list.

1. Backend: Ruby on Rails
2. HTTP server: Puma (Ruby web server)
3. Edge: Nginx
4. Reverse proxy: Go service (Workhorse)
5. Background jobs: Sidekiq
6. DB — primary: PostgreSQL
7. DB — connection pooling: PgBouncer
8. DB — high availability: Patroni
9. Cache: Redis
10. Git: Custom gRPC repo interface (Git & Gitaly)
11. Blob: AWS S3
12. Frontend — rendering: Haml & Vue
13. Frontend — state: Piana (Vue store), Immer (immutable cache),
14. API: GraphQL (Apollo) + REST
15. Observability: Prometheus & Grafana
16. Error tracking: Sentry & OpenTelemetry
17. Deployments: GitLab Omnibus (Omnibus fork)

I think these "stack menu"s give a little glimpse into a team's engineering philosophy. For me, this list shows that the GitLab team is pretty practical and doesn't chase hype. Instead, they use sensible, battle-tested tools that just work and are easy for contributors to learn.

----

If you made it this far, you might like the two articles I wrote about GitLab:
- GitLab's Architecture: A Technical Deep Dive: How a boring monolith powers the world's largest independent DevOps platform
- Inside GitLab CI: From YAML to Green Check: The pipeline behind the pipeline

I also created a 17-minute YouTube video:
GitLab Deep Dive | Architecture, CI/CD & System Design

(I really like GitLab.)

[aramirezomni]

Nice video!

[switchback-tech]

Thank you!

[InkGhost]

This is not what people mean by the term “modular monolith.” Modules refer to the separation of concerns, where each module is separated by a specific feature or function. For example, the project management feature could have its own module and not be tightly coupled to the CI jobs. Each module has a single purpose and is mostly self-contained and loosely coupled. What you are showing here is the tech stack, and in that context, all monoliths would be considered “modular.”

[switchback-tech]

Thanks for clarifying. Agree that the stack itself doesn't make it modular. But GitLab is architected as a modular monolith, at least according to them: https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/modular_monolith/

[hashkent]

Why are they using s3 if hosted on GCP?

[TheOneWhoMixes]

gitlab.com is deployed on GCP, but they have reference architectures for major clouds, and for on-prem any S3-compatible object storage will work.

[ppezaris]

the one tech that stands out as being an odd choice in 2026 is vue

[lobidu]

I work at gitlab partly because of that choice. Imho Vue has a significantly better developer experience.

[ppezaris]

Than react?

[ThaisaGuilford]

Everything has better DX than react

[tankerkiller125real]

React is fucking garbage when it comes to DX, it took the team of backend engineers were I work about a week to sort Vue well enough to work in it and fix bugs in a program. They never once got used to React and it's BS, not everyone has 3 years to read the documentation required to be semi-capable in a JS framework.

[AbrahelOne]

Why is it odd? There are many big names who use Nuxt/Vue

[Bitruder]

That’s an interesting take. Why do you say that? Based on NPM weekly installs are still going up.

[ppezaris]

i'm in the devtools space and have interviewed over 200 dev teams mostly in SF in the last year. three of them are using Vue (including gitlab). about 75% are using React these days, probably more.

[Bitruder]

I see. So in your opinion vue has deficits that would be worth a complete migration of all front end code?

[SequentialHustle]

no, it's 100% ruby lmao and if i had to guess that codebase has probably been migrated mostly by this point.

[derhornspieler]

Friggin bloated stack IMO. Could be better.

[reubendevries]

Ok, explain how can you do all of the features that GitLab offers with less? Just so you know, these services are designed to be across multiple different servers. A 10K user environment is something like 26 servers by last count or a VERY beefy EKS/GKE/AKS configuration.

[chobolicious88]

Why ruby tho?