🚀 A practical Modular Monolith architecture with the latest technologies and architecture like Vertical Slice Architecture, Event Driven Architecture, CQRS, DDD, gRpc, Masstransit, and Aspire in .Net 9.

You can find other version of this project here:

• Booking with Microservices Architecture
• Booking with Monolith Architecture

Table of Contents

• The Goals of This Project
• Technologies - Libraries
• Key Features
• When to Use
• Challenges
• The Domain and Bounded Context - Module Boundary
• Structure of Project
• Development Setup
  • Dotnet Tools Packages
  • Husky
  • Upgrade Nuget Packages
• How to Run
  • Config Certificate
  • Aspire
  • Docker Compose
  • Build
  • Run
  • Test
• Documentation Apis
• Support
• Contribution

The Goals of This Project

• ❇️ Using Vertical Slice Architecture for architecture level.
• ❇️ Using Domain Driven Design (DDD) to implement all business logic.
• ❇️ Using InMemory Broker on top of Masstransit for Event Driven Architecture.
• ❇️ Using gRPC for internal communication.
• ❇️ Using CQRS implementation with MediatR library.
• ❇️ Using Postgres for write side database.
• ❇️ Using MongoDB for read side database.
• ❇️ Using Event Store for write side of Booking Module to store all historical change of aggregate.
• ❇️ Using Inbox Pattern for ensuring message idempotency for receiver and Exactly once Delivery.
• ❇️ Using Outbox Pattern for ensuring no message is lost and there is at At Least One Delivery.
• ❇️ Using Unit Testing for testing small units and mocking our dependencies with Nsubstitute.
• ❇️ Using End-To-End Testing and Integration Testing for testing features with all dependencies using testcontainers.
• ❇️ Using Fluent Validation and a Validation Pipeline Behaviour on top of MediatR.
• ❇️ Using Minimal API for all endpoints.
• ❇️ Using AspNetCore OpenApi for generating built-in support OpenAPI documentation in ASP.NET Core.
• ❇️ Using Health Check for reporting the health of app infrastructure components.
• ❇️ Using Docker-Compose and Kubernetes for our deployment mechanism.
• ❇️ Using Kibana on top of Serilog for logging.
• ❇️ Using OpenTelemetry for distributed tracing on top of Jaeger.
• ❇️ Using OpenTelemetry for monitoring on top of Prometheus and Grafana.
• ❇️ Using IdentityServer for authentication and authorization base on OpenID-Connect and OAuth2.
• ❇️ Using Aspire for service discovery, observability, and local orchestration of microservices.

Technologies - Libraries

• ✔️ .NET 9 - .NET Framework and .NET Core, including ASP.NET and ASP.NET Core.
• ✔️ MVC Versioning API - Set of libraries which add service API versioning to ASP.NET Web API, OData with ASP.NET Web API, and ASP.NET Core.
• ✔️ EF Core - Modern object-database mapper for .NET. It supports LINQ queries, change tracking, updates, and schema migrations.
• ✔️ AspNetCore OpenApi - Provides built-in support for OpenAPI document generation in ASP.NET Core.
• ✔️ Masstransit - Distributed Application Framework for .NET.
• ✔️ MediatR - Simple, unambitious mediator implementation in .NET.
• ✔️ FluentValidation - Popular .NET validation library for building strongly-typed validation rules.
• ✔️ Scalar - Scalar provides an easy way to render beautiful API references based on OpenAPI/Swagger documents.
• ✔️ Swagger UI - Swagger tools for documenting API's built on ASP.NET Core.
• ✔️ Serilog - Simple .NET logging with fully-structured events
• ✔️ Polly - Polly is a .NET resilience and transient-fault-handling library that allows developers to express policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback in a fluent and thread-safe manner.
• ✔️ Scrutor - Assembly scanning and decoration extensions for Microsoft.Extensions.DependencyInjection
• ✔️ Opentelemetry-dotnet - The OpenTelemetry .NET Client
• ✔️ DuendeSoftware IdentityServer - The most flexible and standards-compliant OpenID Connect and OAuth 2.x framework for ASP.NET Core.
• ✔️ EasyCaching - Open source caching library that contains basic usages and some advanced usages of caching which can help us to handle caching more easier.
• ✔️ Mapster - Convention-based object-object mapper in .NET.
• ✔️ Hellang.Middleware.ProblemDetails - A middleware for handling exception in .Net Core.
• ✔️ NewId - NewId can be used as an embedded unique ID generator that produces 128 bit (16 bytes) sequential IDs.
• ✔️ Yarp - Reverse proxy toolkit for building fast proxy servers in .NET.
• ✔️ gRPC-dotnet - gRPC functionality for .NET.
• ✔️ EventStore - The open-source, functional database with Complex Event Processing.
• ✔️ MongoDB.Driver - .NET Driver for MongoDB.
• ✔️ xUnit.net - A free, open source, community-focused unit testing tool for the .NET Framework.
• ✔️ Respawn - Respawn is a small utility to help in resetting test databases to a clean state.
• ✔️ Testcontainers - Testcontainers for .NET is a library to support tests with throwaway instances of Docker containers.
• ✔️ K6 - Modern load testing for developers and testers in the DevOps era.
• ✔️ Aspire - .NET stack for building and orchestrating observable, distributed cloud-native applications.

Key Features

1. Modular Design: The application is divided into modules, each responsible for a specific functionality.
2. Loose Coupling: Modules interact through well-defined interfaces, improving maintainability.
3. Single Deployment: The entire application is still deployed as one unit.
4. Shared Database: Typically uses a single database, but modules can have their own schemas or tables.

When to Use

1. Medium to Large Projects: Suitable for applications with growing complexity but not ready for microservices.
2. Better Maintainability: Ideal for teams wanting a more organized and maintainable codebase than a traditional monolith.
3. Future-Proofing: A stepping stone toward microservices, allowing teams to prepare for future scalability.
4. Single Team or Small Teams: Works well for teams that want modularity without the overhead of distributed systems.

Challenges

• Still a single deployment unit, so scaling is limited.
• Requires careful design to avoid tight coupling between modules.
• Not as scalable or fault-tolerant as microservices.

The Domain And Bounded Context - Module Boundary

• Identity Module: The Identity Module is a bounded context for the authentication and authorization of users using Identity Server. This service is responsible for creating new users and their corresponding roles and permissions using .Net Core Identity and Jwt authentication and authorization.

• Flight Module: The Flight Module is a bounded context CRUD service to handle flight related operations.

• Passenger Module: The Passenger Module is a bounded context for managing passenger information, tracking activities and subscribing to get notification for out of stock products.

• Booking Module: The Booking Module is a bounded context for managing all operation related to booking ticket.

Structure of Project

In this project, I used vertical slice architecture at the architectural level and feature folder structure to structure my files.

I treat each request as a distinct use case or slice, encapsulating and grouping all concerns from front-end to back. When adding or changing a feature in an application in n-tire architecture, we are typically touching many "layers" in an application. We are changing the user interface, adding fields to models, modifying validation, and so on. Instead of coupling across a layer, we couple vertically along a slice. We minimize coupling between slices, and maximize coupling in a slice.

With this approach, each of our vertical slices can decide for itself how to best fulfill the request. New features only add code, we're not changing shared code and worrying about side effects.

Instead of grouping related action methods in one controller, as found in traditional ASP.net controllers, I used the REPR pattern. Each action gets its own small endpoint, consisting of a route, the action, and an IMediator instance (see MediatR). The request is passed to the IMediator instance, routed through a Mediatr pipeline where custom middleware can log, validate and intercept requests. The request is then handled by a request specific IRequestHandler which performs business logic before returning the result.

The use of the mediator pattern in my controllers creates clean and thin controllers. By separating action logic into individual handlers we support the Single Responsibility Principle and Don't Repeat Yourself principles, this is because traditional controllers tend to become bloated with large action methods and several injected Services only being used by a few methods.

I used CQRS to decompose my features into small parts that makes our application:

• Maximize performance, scalability and simplicity.
• Easy to maintain and add features to. Changes only affect one command or query, avoiding breaking changes or creating side effects.
• It gives us better separation of concerns and cross-cutting concern (with help of mediatr behavior pipelines), instead of bloated service classes doing many things.

Using the CQRS pattern, we cut each business functionality into vertical slices, for each of these slices we group classes (see technical folders structure) specific to that feature together (command, handlers, infrastructure, repository, controllers, etc). In our CQRS pattern each command/query handler is a separate slice. This is where you can reduce coupling between layers. Each handler can be a separated code unit, even copy/pasted. Thanks to that, we can tune down the specific method to not follow general conventions (e.g. use custom SQL query or even different storage). In a traditional layered architecture, when we change the core generic mechanism in one layer, it can impact all methods.

Development Setup

Dotnet Tools Packages

For installing our requirement packages with .NET cli tools, we need to install dotnet tool manifest.

dotnet new tool-manifest

And after that we can restore our dotnet tools packages with .NET cli tools from .config folder and dotnet-tools.json file.

dotnet tool restore

Husky

Here we use husky to handel some pre commit rules and we used conventional commits rules and formatting as pre commit rules, here in package.json. of course, we can add more rules for pre commit in future. (find more about husky in the documentation) We need to install husky package for manage pre commits hooks and also I add two packages @commitlint/cli and @commitlint/config-conventional for handling conventional commits rules in package.json. Run the command bellow in the root of project to install all npm dependencies related to husky:

npm install

Note: In the root of project we have .husky folder and it has commit-msg file for handling conventional commits rules with provide user friendly message and pre-commit file that we can run our scripts as a pre-commit hooks. that here we call format script from package.json for formatting purpose.

Upgrade Nuget Packages

For upgrading our nuget packages to last version, we use the great package dotnet-outdated. Run the command below in the root of project to upgrade all of packages to last version:

dotnet outdated -u

How to Run

Config Certificate

Run the following commands to Config SSL in your system:

Windows using Linux containers

dotnet dev-certs https -ep %USERPROFILE%\.aspnet\https\aspnetapp.pfx -p password
dotnet dev-certs https --trust

Note: for running this command in powershell use $env:USERPROFILE instead of %USERPROFILE%

macOS or Linux

dotnet dev-certs https -ep ${HOME}/.aspnet/https/aspnetapp.pfx -p $CREDENTIAL_PLACEHOLDER$
dotnet dev-certs https --trust

Aspire

To run the application using the Aspire App Host, execute the following command from the solution root:

aspire run

Note:The Aspire dashboard will be available at http://localhost:18888

Docker Compose

To run this app in Docker, use the docker-compose.yaml and execute the below command at the root of the application:

docker-compose -f ./deployments/docker-compose/docker-compose.yaml up -d

Build

To build all modules, run this command in the root of the project:

dotnet build

Run

To run all modules, run this command in the root of the Api folder:

dotnet run

Test

To test all modules, run this command in the root of the project:

dotnet test

Documentation Apis

For checking API documentation, navigate to /swagger for Swagger OpenAPI or /scalar/v1 for Scalar OpenAPI to visit list of endpoints.

As part of API testing, I created the booking.rest file which can be run with the REST Client VSCode plugin.

Support

If you like my work, feel free to:

• ⭐ this repository. And we will be happy together :)

Thanks a bunch for supporting me!

Contribution

Thanks to all contributors, you're awesome and this wouldn't be possible without you! The goal is to build a categorized, community-driven collection of very well-known resources.

Please follow this contribution guideline to submit a pull request or create the issue.

Project References & Credits

• https://github.com/jbogard/ContosoUniversityDotNetCore-Pages
• https://github.com/kgrzybek/modular-monolith-with-ddd
• https://github.com/oskardudycz/EventSourcing.NetCore
• https://github.com/thangchung/clean-architecture-dotnet
• https://github.com/pdevito3/MessageBusTestingInMemHarness

License

This project is made available under the MIT license. See LICENSE for details.