Alexander Stathis: Scaling a Modular Rails Monolith at AngelList

In this episode of On Rails, Robby is joined by Alexander Stathis, a Principal Software Engineer at AngelList, where Rails powers complex investment, accounting, and banking business logic across a modular monolith structure. They explore how AngelList maintains conceptual boundaries in their codebase, uses gradual typing to influence their Ruby style away from Rails “magic,” and why they’ve adopted multiple async job solutions for different types of work rather than seeking a one-size-fits-all approach. Alex shares insights on consolidating microservices back into their monolith, creating the Boba gem to extend type generation capabilities, using production data subsetting tools for local development, and successfully onboarding engineers without Rails experience in under a month while staying current on Ruby 3.4 and Rails 7.2.

Tools & Libraries Mentioned

Active Job – Framework-agnostic job API built into Rails.

ASDF – Tool version manager.

Boba – AngelList’s Sorbet compiler extension.

Delayed Job – Database-backed job processor.

FactoryBot – Test data builder.

GoodJob – Postgres-backed Active Job processor.

GraphQL Batch Loader – Batching utility for GraphQL.

GraphQL Ruby – Ruby GraphQL implementation.

Linear – Issue tracking tool.

Money – currency handling library.

Packwerk – Shopify’s modular boundary enforcement tool.

Paperclip – Legacy file attachment gem for Rails (deprecated).

RSpec – Ruby testing framework.

Sidekiq – Redis-backed job framework.

Solid Queue – Rails 8 Active Job adapter.

Sorbet – Gradual static type checker for Ruby.

State Machines – Finite state machine support.

Tapioca – Sorbet RBI file generator.

Temporal – Workflow orchestration system.

Tonic – De-identified datasets platform.

Will Lars

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On Rails is a podcast focused on real-world technical decision-making, exploring how teams are scaling, architecting, and solving complex challenges with Rails.

On Rails is brought to you by The Rails Foundation, and hosted by Robby Russell of Planet Argon, a consultancy that helps teams modernize their Ruby on Rails applications.