CSharpModulith

A modular monolith built with .NET 10, ASP.NET Core, and .NET Aspire. Each business capability lives in its own project, enforced by ArchUnitNET architecture tests.

Solution Structure

src/
├── CSharpModulith.Host/                  # ASP.NET Core composition root and HTTP pipeline
├── CSharpModulith.AppHost/               # .NET Aspire orchestration (local dev)
├── CSharpModulith.ServiceDefaults/       # Shared service defaults (OpenTelemetry, health, etc.)
├── CSharpModulith.Shared/                # Shared kernel
├── CSharpModulith.Capability.Order/      # Order capability
├── CSharpModulith.Capability.Payment/    # Payment capability
└── CSharpModulith.Capability.Todos/      # Todos capability

tests/
├── CSharpModulith.Architecture.Tests/    # ArchUnitNET architecture rules
├── CSharpModulith.Capability.Order.Tests/
├── CSharpModulith.Capability.Payment.Tests/
└── CSharpModulith.Capability.Todos.Tests/

Tech Stack

• .NET 10 / C# (latest)
• ASP.NET Core (Host)
• .NET Aspire (local orchestration, service defaults)
• PostgreSQL (primary database, via Aspire)
• SQLite (fallback when PostgreSQL is not configured)
• RabbitMQ (messaging)
• MailPit (local email testing)
• Entity Framework Core (persistence)
• ArchUnitNET (architecture tests)
• xUnit (test framework)
• Docker / Docker Compose (containerized development)

Prerequisites

• Docker and Docker Compose

No local .NET SDK installation is required. All build, test, and run commands execute inside a Docker container.

Getting Started

Build the dev image and start the stack:

make up

The HTTP API (Compose service api) is at http://localhost:8080 (override published port with MODULITH_HOST_PORT). The Blazor UI defaults to http://localhost:5040 (MODULITH_FRONTEND_PORT).

For Compose, the frontend container uses network_mode: service:api, so it shares the API container’s network stack and calls http://127.0.0.1:8080 (no cross-container routing or DNS). The published Blazor port is mapped on the api service (5040→8081); see docker-compose.yml.

Common Commands

Command	Description
make up	Build and start the full stack (detached)
make run	Build and start in the foreground
make down	Stop and remove containers
make logs	Follow container logs
make shell	Interactive shell in the .NET SDK container
make test	Run all tests
make build-app	Build the solution inside the container
make build-dev-image	Rebuild the dev SDK image
make clean	Stop containers, remove images and build artifacts

Running SDK Commands Directly

docker compose exec -T csharp dotnet build CSharpModulith.sln -c Release
docker compose exec -T csharp dotnet test CSharpModulith.sln -c Release
docker compose exec -T csharp dotnet format

Aspire AppHost (Local Dev)

For local orchestration with the Aspire dashboard, run the AppHost directly (requires a local .NET 10 SDK):

dotnet run --project src/CSharpModulith.AppHost

This starts PostgreSQL, RabbitMQ, SQLite, and MailPit as Aspire resources alongside the Host.

Architecture

Each capability is an independent class library project (CSharpModulith.Capability.<Name>) following a layered structure:

• Domain -- aggregates, entities, value objects, domain events, repository contracts
• Application -- use cases, facades, read models, queries, bridge interfaces
• Infrastructure -- persistence, messaging, bridge implementations
• Presentation -- HTTP endpoints, view models, request/response DTOs

Cross-capability communication goes through bridges: an interface declared in the consuming capability's application layer, implemented in its infrastructure layer using the other capability's facade.

Architecture rules are enforced at build time via ArchUnitNET tests in tests/CSharpModulith.Architecture.Tests/.

License

Copyright (c) 2026 Florian Krämer. Licensed under the MIT License.