What Are the Most Common Design Patterns in Backend Development?

Common Backend Design Patterns

Creational

Singleton Ensures a class has only one instance; provides a global access point

• Used for: database connection pool, Logger, config manager
• Caveat: needs thread safety in multi-threaded environments

Factory Encapsulates object creation; creates different subclasses based on conditions

• Used for: payment methods (CreditCard/PayPal), notification services (Email/SMS)

Structural

Adapter Makes incompatible interfaces work together without modifying original code

• Used for: third-party SDK integration, bridging old and new systems

Decorator Dynamically adds behavior to objects without modifying the original class

• Used for: logging, caching, validation

Behavioral

Observer Notifies all subscribers when an object's state changes

• Used for: event systems, message queues, webhooks

Strategy Encapsulates interchangeable algorithms; switch at runtime

• Used for: sorting strategies, pricing rules, auth mechanisms

Command Encapsulates a request as an object; supports undo/redo and queuing

• Used for: task queues, operation history