Posted 5 months ago. Visible to the public. Linked content.

Structuring Rails applications: the Modular Monorepo Monolith

Root Insurance runs their application as a monolithic Rails application – but they've modularized it inside its repository. Here is their approach in summary:


  • Keep all code in a single repository (monorepo)
  • Have a Rails Engine for each logical component instead of writing a single big Rails Application
  • Build database-independent components as gems
  • Thus: gems/ and engines/ directories instead of app/
  • Define a dependency graph of components. It should have few edges.
  • Gems and Engines can be extracted easier once necessary.

Advantages over a classic Rails monolith

  • By (automatically) only requiring expected/allowed dependencies in tests, components cannot accidentally use (i.e. depend on) code they're not allowed to
  • Onboarding is easier because of the clear separation and dependencies. No need to know the whole application.
  • Faster test runs, because only dependent components need to run.
  • A growing team can still keep up the development pace because developers concentrate on specific components. Merge requests target a specific component.

Advantages over a distributed application setup (multiple repositories, multiple applications)

  • Everything is still deployed at once. No need to orchestrate branch merges and deploys across N repos.

Other resources


Does your version of Ruby on Rails still receive security updates?
Rails LTS provides security patches for old versions of Ruby on Rails (3.2 and 2.3).

Owner of this card:

Dominik Schöler
Last edit:
about 1 month ago
by Dominik Schöler
About this deck:
We are makandra and do test-driven, agile Ruby on Rails software development.
License for source code
Posted by Dominik Schöler to makandra dev
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