Monica Application Modular Monolith

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](references/00-solution-layout.md) to understand the target domain-first structure.
2. Use [01-create-subdomain-and-domain.md](references/01-create-subdomain-and-domain.md) when adding a new bounded context.
3. Use [02-protocol-platform-and-internal-collaboration.md](references/02-protocol-platform-and-internal-collaboration.md) before introducing cross-domain requests, DTOs, or events.
4. Use [03-boundaries-dependencies-and-persistence.md](references/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](references/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.
• When a domain exposes ApplicationService HTTP endpoints through default routing, keep one assembly-level AutoControllerConfig(DefaultRoutePrefix = "api/v1", DomainName = "{Subdomain}") file in the domain project root instead of repeating class-level Route attributes on every handler.
• AppHost entry projects are composition-only entry points. Keep them down to the project file and Program.cs; do not place business ProjectUnits there.
• When AppHost composition needs a Configuration ProjectUnit during registration, register Mo.AddConfiguration(...) first and call Mo.RegisterInstantly(builder) before later registrations depend on those options.
• 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](references/00-solution-layout.md)
• New subdomain/domain workflow: [01-create-subdomain-and-domain.md](references/01-create-subdomain-and-domain.md)
• Protocol platform and collaboration: [02-protocol-platform-and-internal-collaboration.md](references/02-protocol-platform-and-internal-collaboration.md)
• Boundaries, dependencies, and persistence: [03-boundaries-dependencies-and-persistence.md](references/03-boundaries-dependencies-and-persistence.md)
• Completion checklist: [04-delivery-checklist.md](references/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.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Tairitsua
• Source: Tairitsua/Monica
• License: MIT
• Homepage: https://monica.dpdns.org/

Install and usage instructions live in the source repository linked above.