When starting a web app with unclear requirements, balance scalability and simplicity. Here’s how to do it in C# without overcomplicating:

1. Start Simple, but Plan for Growth

  • Build a modular core: Split your app into layers (e.g., Presentation, Business Logic, Data Access). Use interfaces and dependency injection (e.g., ASP.NET Core’s built-in DI) to keep components loosely coupled. 
// Example: Interface for flexibility
  public interface IUserService 
  {
      Task<User> GetUserAsync(int id);
  }
  • Avoid early optimization: Use a monolithic design first. Split into microservices only when traffic or complexity demands it.

2. Focus on Risky Areas

Identify parts likely to change (e.g., payment gateways, third-party integrations). Make these replaceable:

// Abstract payment processing
public interface IPaymentProcessor 
{
    Task ProcessPaymentAsync(decimal amount);
}

// Start with a simple implementation
public class BasicPaymentProcessor : IPaymentProcessor { ... }

Leave stable parts (e.g., user authentication) straightforward.

3. Use Proven Tools

  • Stick to common frameworks: ASP.NET Core, Entity Framework Core, and Azure services are battle-tested and scale well.
  • Avoid custom solutions for problems like caching or logging. Use built-in middleware or libraries (e.g., Serilog for logging).

4. Delay Decisions

  • Database choice: Start with SQL Server or PostgreSQL. Use the Repository Pattern to hide database details, making it easier to switch later. 
public class UserRepository : IUserRepository 
  {
      // Entity Framework Core example
      public async Task<User> GetByIdAsync(int id) 
      {
          return await _context.Users.FindAsync(id);
      }
  }
  • Infrastructure: Build for a single server first. Use cloud services (e.g., Azure App Service) to scale horizontally later.

5. Write Just Enough Tests

  • Cover critical workflows (e.g., payment processing) with unit tests. Avoid testing every small method early.
  • Use tools like xUnit or NUnit for maintainable tests.

6. Iterate and Refactor

  • Release a minimal viable product (MVP) first. Gather feedback before adding complex features.
  • Refactor when requirements stabilize. For example:
    • Replace a basic IPaymentProcessor with a more robust solution.
    • Split the monolith into microservices only if needed.

Avoid Over-Engineering

🚩 Red flags:

  • Adding layers (e.g., extra abstractions, “just-in-case” microservices) before they’re needed.
  • Building custom frameworks instead of using existing tools.
  • Over-designing databases for hypothetical future needs.

Key Takeaway

Build for today, design for tomorrow:

  • Keep code clean and modular.
  • Use abstractions only where change is likely.
  • Scale when the problem arises, not before.

By focusing on flexibility and simplicity, you’ll avoid over-engineering while staying ready to scale.