🪁 Monolith To Cloud Architecture

A practical architecture styles for migrating from monolith to modern cloud native application with the latest technologies and architectures like Vertical Slice Architecture, Event Sourcing, CQRS, DDD, gRpc, MongoDB, RabbitMq, and Masstransit in .Net 9.

Table of Contents

• The Goals of This Project
• Technologies - Libraries
• Architectural Styles and How to Choose the Right One
  • 1. Monolithic Architecture
  • 2. Modular Monolith Architecture
  • 3. Microservices Architecture
• The Domain and Bounded Context - Service Boundary
• Structure of Project
• 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 Rabbitmq 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 Microservice/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 Yarp as a microservices gateway.
• ❇️ Using Kubernetes to achieve efficient scaling and ensure high availability for each of our microservices.
• ❇️ Using Nginx Ingress Controller for load balancing between our microservices top of Kubernetes.
• ❇️ Using cert-manager to Configure TLS in kubernetes cluster.

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.
• ✔️ Tye - Developer tool that makes developing, testing, and deploying microservices and distributed applications easier.
• ✔️ 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.

Architectural Styles and How to Choose the Right One

The repository is organized into three folders, each representing a different architectural style. Below is an overview of each style, along with guidance on when to choose it based on your project requirements, team size, scalability needs, and long-term maintenance goals.

1. Monolithic Architecture Style

A traditional monolithic architecture where all components of the application are tightly coupled and deployed as a single unit.

• When to Choose:
  • Your project is small or medium-sized.
  • You have a small development team.
  • You need to develop and deploy the application quickly.
  • The application has relatively simple functionality.
  • You don’t anticipate significant scaling needs in the near future.
• Pros:
  • Simple to develop, test, and deploy.
  • Easier to manage for small teams.
  • Lower operational overhead.
• Cons:
  • Tight coupling makes it harder to maintain as the codebase grows.
  • Scaling is limited to scaling the entire application.
  • Difficult to adopt new technologies or frameworks incrementally.

2. Modular Monolith Architecture Style

A modular monolith architecture where the application is divided into modules, but still deployed as a single unit. This approach promotes better separation of concerns and maintainability.

• When to Choose:
  • Your project is medium to large-sized.
  • You want better separation of concerns and maintainability than a traditional monolith.
  • You plan to scale the application in the future but want to avoid the complexity of microservices.
  • Your team is growing, and you need a more organized codebase.
• Pros:
  • Better separation of concerns compared to a traditional monolith.
  • Easier to maintain and extend as the application grows.
  • Can be a stepping stone toward a microservices architecture.
  • Simpler deployment than microservices.
• Cons:
  • Still a single deployment unit, so scaling is limited.
  • Requires careful design to avoid tight coupling between modules.

3. Microservices Architecture Style

A microservices architecture where the application is broken down into small, independent services that can be developed, deployed, and scaled independently.

• When to Choose:
  • Your project is large and complex.
  • You need to scale different parts of the application independently.
  • Your team is large and can handle the complexity of distributed systems.
  • You need to adopt different technologies or frameworks for different parts of the application.
  • You require high availability and fault tolerance.
• Pros:
  • Independent development, deployment, and scaling of services.
  • Better fault isolation.
  • Flexibility to use different technologies for different services.
  • Easier to maintain and update individual services.
• Cons:
  • Higher complexity in development, testing, and deployment.
  • Requires robust DevOps practices and infrastructure.
  • Increased operational overhead (e.g., monitoring, logging, service discovery).

The Domain And Bounded Context - Service Boundary

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

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

• Booking Service: The Booking Service 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.

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.