Modular Monolith

Use this when the app is organized into named packages, packs, engines, or bounded contexts.

architecture :modular_monolith,
  components: {
    billing: "packs/billing/**/*.rb",
    catalog: "packs/catalog/**/*.rb",
    shared: "packs/shared/**/*.rb"
  },
  allow: {
    billing: %i[shared],
    catalog: %i[shared]
  }

Every component gets an allowlist. If a component is omitted from allow, it may not depend on any other declared component.

Add public to force other packs through a front door instead of reaching into internals:

architecture :modular_monolith,
  components: {
    billing: "packs/billing/**/*.rb",
    catalog: "packs/catalog/**/*.rb"
  },
  allow: {
    catalog: %i[billing]
  },
  public: {
    billing: "packs/billing/app/public/**/*.rb"
  }

catalog may depend on billing, but only on constants defined under billing’s public files. See Public API.

Alias:

architecture :bounded_contexts, components: { ... }, allow: { ... }

ArchSpec also adds a cycle check across the declared components.

Engines and Packs

Engines and packs are the same topology: named packages under a parent directory. Rather than list them by hand, declare one component per subdirectory with each_directory. It resolves paths against the Archspec.rb location, so it works no matter where archspec runs from.

each_directory "engines/*" do |name, path|
  component name, in: "#{path}/**/*.rb"
end

component :shared, in: "engines/shared/**/*.rb"

billing.can_use :shared
catalog.can_use :shared
no_cycles!

Archspec.rb is plain Ruby, so you keep full control: skip a directory, rename a component, or attach different rules per package inside the block.