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Structured Interview Pack
How to Structure a Maintainable Backend Application
A pragmatic blueprint for structuring scalable backend applications using Clean Layered Architecture, separating transport protocols from business domain rules, and avoiding both spaghetti code and enterprise over-engineering.
The Dependency Inversion Principle dictates that high-level business rules must never depend on low-level implementation details (such as HTTP routing libraries or database drivers). Both should depend on abstractions.
Organize code by business feature/domain (e.g. `orders/`, `billing/`, `users/`) rather than technical type (`controllers/`, `models/`). Features that change together should live together.
- Master the 3-Layer Architecture: Controllers (Transport), Services (Domain), and Repositories (Data)
- Decouple business rules from frameworks, HTTP protocols, and database ORMs
- Compare Feature-based directory organization (Screaming Architecture) vs Technical-Layer organization
- Model domain errors cleanly without polluting business logic with HTTP status codes
1. The Anti-Pattern: The Anemic Fat Controller
Free Chapter PreviewIn early-stage projects, engineers frequently place everything inside a single route handler:
- Parsing request parameters.
- Validating business logic.
- Executing raw SQL queries.
- Calculating pricing and discounts.
- Sending email notifications.
- Formatting JSON responses.
Why this collapses in production:
- 1Zero Reusability: If an internal cron job or CLI command needs to execute the same checkout logic, it cannot do so without simulating an HTTP request.
- 2Untestable: Writing unit tests requires mocking the entire HTTP request/response object and database connection.
- 3Merge Conflict Magnet: Multiple developers modifying the same monolithic route file step on each other's changes.
2. The Clean 3-Tier Layered Blueprint
In this section, we examine the production failure mechanics, internal socket buffers, and kernel-level trace diagnostics...
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