monica-application-modular-monolith

name

monica-application-modular-monolith

description

DDD modular monolith architecture guidance for Monica application projects. Use when creating or extending a bounded context under Domains, planning the strict solution-project dependency chain across Platform layers, placing project-common versus subdomain-only library references, shaping Platform.Protocol/PublishedLanguages, defining domain-owned Application layout, merged domain packages, and host composition, or deciding collaboration boundaries inside a single deployment. Pair with monica-application-project-unit-development for unit-level implementation.

Monica Application Modular Monolith

Overview

Use this skill to structure a Monica application solution as a modular monolith with explicit subdomain boundaries. It keeps the deployment single while preserving contract-first collaboration and clear ownership per bounded context.

Workflow

1. Read 00-solution-layout.md to understand the target domain-first structure.
2. Use 01-create-subdomain-and-domain.md when adding a new bounded context.
3. Use 02-protocol-platform-and-internal-collaboration.md before introducing cross-domain requests, DTOs, or events.
4. Use 03-boundaries-dependencies-and-persistence.md to keep host composition and persistence ownership coherent.
5. Hand unit implementation to monica-application-project-unit-development, then finish with 04-delivery-checklist.md.

Core Rules

• Split the solution by bounded context under Domains/, not by global Application, Domain, or Infrastructure buckets.
• Each bounded context under Domains/ uses a single Domains.{Subdomain}.csproj that keeps Application, domain models, and domain-owned infrastructure together.
• Keep the shared platform split explicit: Platform.BuildingBlocks for project-agnostic infrastructure extensions, Platform.Infrastructure for solution-owned infrastructure wiring, and Platform.Protocol for shared business language.
• Use the strict solution-project reference chain AppHost -> Domains.{Subdomain} -> Platform.Infrastructure -> Platform.Protocol -> Platform.BuildingBlocks.
• Put project-common library references in Platform.BuildingBlocks. Keep subdomain-only package references in the owning Domains.{Subdomain}.csproj.
• Keep cross-domain dependencies pointed at Shared/Platform.Protocol/PublishedLanguages, consuming shared Contracts/ and only the deliberate Implementations/* surfaces exposed there. Do not reference another domain's internal implementation directly.
• Keep domain-owned application units in Application/HandlersCommand, Application/HandlersQuery, Application/HandlersEvent, and Application/BackgroundWorkers.
• Keep repository implementations and DbContext-related files in Repository/, and keep pure helper code in Utilities/ with Utils* names.
• Declare every ApplicationService endpoint on its Command* or Query* request with [ApiEndpoint]; handlers contain behavior, not MVC route or binding attributes.
• A request in strict Platform.Protocol.PublishedLanguages.Domain{Subdomain}.Requests with [ApiEndpoint] is published HTTP/RPC language and generates I{Subdomain}CommandApi or I{Subdomain}QueryApi. A request local to the domain project generates HTTP only.
• Keep one WebApiGenerationConfig("api/v1", DomainName = "{Subdomain}") in each domain assembly for local endpoints, and configure published RPC targets in Platform.Protocol. Do not use RPC metadata snapshots or source-tree export tasks.
• AppHost entry projects are composition-only entry points. Keep them down to the project file and Program.cs; do not place business ProjectUnits there.
• Register monica.AddConfiguration() inside the AppHost's single builder.AddMonica(...) callback. Read bootstrap values from builder.Configuration during composition; consume Configuration ProjectUnits through typed options injection at runtime.
• Keep .slnx solution folders aligned with the physical layout under src/AppHost, src/Shared, and src/Domains.
• Treat the modular monolith as one deployment, not as hidden microservices in the same repository.

Reference Navigation

• Solution structure: 00-solution-layout.md
• New subdomain/domain workflow: 01-create-subdomain-and-domain.md
• Protocol platform and collaboration: 02-protocol-platform-and-internal-collaboration.md
• Boundaries, dependencies, and persistence: 03-boundaries-dependencies-and-persistence.md
• Completion checklist: 04-delivery-checklist.md

Scope Notes

• This skill defines domain boundaries and composition rules inside one deployment.
• Use monica-application-project-unit-development whenever the next step is to implement requests, handlers, entities, repositories, events, configurations, or jobs.