Modular Monolith

A modular monolith keeps one deployable application while giving business modules explicit ownership and dependency boundaries. Modules should not reach into another module’s infrastructure.

src/app/
├── billing/{domain,application,infrastructure}/
└── identity/{domain,application,infrastructure}/

Complete Configuration

deply:
  paths: ["."]
  exclude_files:
    - '.*/\.venv/.*'
    - '.*/tests?/.*'
  layers:
    - name: billing_domain
      collectors:
        - type: directory
          directories: ["src/app/billing/domain"]
    - name: billing_application
      collectors:
        - type: directory
          directories: ["src/app/billing/application"]
    - name: billing_infrastructure
      collectors:
        - type: directory
          directories: ["src/app/billing/infrastructure"]
    - name: identity_domain
      collectors:
        - type: directory
          directories: ["src/app/identity/domain"]
    - name: identity_application
      collectors:
        - type: directory
          directories: ["src/app/identity/application"]
    - name: identity_infrastructure
      collectors:
        - type: directory
          directories: ["src/app/identity/infrastructure"]
  ruleset:
    billing_domain:
      disallow_layer_dependencies: [billing_application, billing_infrastructure, identity_domain, identity_application, identity_infrastructure]
    billing_application:
      disallow_layer_dependencies: [billing_infrastructure, identity_domain, identity_application, identity_infrastructure]
    billing_infrastructure:
      disallow_layer_dependencies: [identity_domain, identity_application, identity_infrastructure]
    identity_domain:
      disallow_layer_dependencies: [identity_application, identity_infrastructure, billing_domain, billing_application, billing_infrastructure]
    identity_application:
      disallow_layer_dependencies: [identity_infrastructure, billing_domain, billing_application, billing_infrastructure]
    identity_infrastructure:
      disallow_layer_dependencies: [billing_domain, billing_application, billing_infrastructure]

If modules collaborate through explicit application APIs, model those APIs as separate layers rather than allowing imports into an entire sibling module. Deply does not prove transactional or deployment boundaries.

Validate

deply validate --config=deply.yaml
deply analyze --parallel --config=deply.yaml

Reference: Modular Monolith architecture.