Clean Architecture & SOLID Principles

Mastery of .NET Core extends beyond knowing APIs and framework features — it involves understanding architectural patterns, design principles, team collaboration practices, and the professional judgment required to make sound technical decisions in complex, real-world environments. Senior .NET Core developers are distinguished not by the volume of code they write but by the quality, maintainability, and scalability of the systems they design. This module covers the advanced topics and professional best practices that separate competent .NET Core developers from exceptional ones who are sought after for senior and architect roles. BackgroundService and the IHostedService interface enable long-running background tasks in .NET Core applications. Worker Services — .NET Core applications without an HTTP listener — use BackgroundService as the base class for tasks like message queue consumers, scheduled data processing, event-driven workflows, and health monitoring. The Generic Host (IHost) provides the unified hosting infrastructure for both web applications and worker services, with built-in dependency injection, configuration, logging, and graceful shutdown support. System.Threading.Channels provides high-performance, thread-safe producer-consumer queues for inter-thread communication within a single process, ideal for decoupling fast producers from slow consumers without introducing external message broker complexity. SignalR is ASP.NET Core's library for adding real-time web functionality — the ability to push content from server to connected clients instantly. It abstracts over WebSockets, Server-Sent Events, and Long Polling, automatically choosing the best transport for the client and network conditions. SignalR Hubs define methods that clients can call (RPC-style) and methods the server can call on connected clients. Real-time applications built with SignalR include live dashboards, collaborative editing tools, chat applications, live notifications, live-streaming data feeds, and multiplayer games. Azure SignalR Service provides managed scale-out for SignalR, maintaining WebSocket connections with millions of simultaneous users without requiring sticky sessions or complex server coordination. The CQRS (Command Query Responsibility Segregation) pattern separates read operations (queries) from write operations (commands), allowing each to be optimized independently. In a CQRS architecture, commands express user intent to change system state and are handled by command handlers that enforce business rules before persisting changes. Queries retrieve read model projections optimized for the specific needs of each screen or API consumer, using denormalized views, caches, or read-optimized databases. MediatR, a popular .NET library, implements the mediator pattern to dispatch commands and queries to their handlers, decoupling the application layer from the infrastructure layer. Event Sourcing complements CQRS by persisting all state changes as an immutable sequence of events — the current state is derived by replaying events — providing a complete audit log, enabling temporal queries, and supporting event-driven integration with other systems.

Clean Architecture is a software design philosophy that separates the business logic from external concerns like databases, frameworks, and user interfaces.