error-handling-patterns

Error handling patterns provide structured approaches using custom exceptions, Result types, and Polly resilience policies to handle both unexpected errors and expected failures. Implement custom exception hierarchies for exceptional cases, Result types for recoverable failures, and Polly policies with retry, circuit breaker, and fallback mechanisms to ensure applications recover gracefully from service disruptions.

Exceptions represent unexpected, exceptional conditions that interrupt normal flow; Result types represent expected, recoverable failures as values. Use exceptions for truly exceptional scenarios and custom exception hierarchies for domain-specific errors. Use Result types to model operations that may predictably fail, promoting explicit error handling and clearer API contracts.

Polly resilience policies automate recovery logic for external service calls and database operations. Define retry policies with exponential backoff to handle transient failures, circuit breakers to prevent cascading failures, and fallback mechanisms to provide alternative responses. Combine these policies to build stable applications that degrade gracefully when dependencies become unreliable.

Error handling patterns apply across .NET (C#) and TypeScript environments, though implementations differ by language. Use custom exception hierarchies and Result types in both; Polly is .NET-specific, but TypeScript has equivalent resilience libraries. The underlying principles—retry logic, circuit breakers, and graceful degradation—translate across both platforms.

Graceful degradation ensures core functionality remains available when non-critical services fail, improving user experience during outages. Implement fallback responses, cached data, or reduced feature sets when dependencies are unavailable. Use this pattern for background processing, API integrations, and service meshes where partial availability is preferable to complete failure.

Consistent error handling in API design uses custom exception hierarchies, Result type wrappers, and observability to communicate failures predictably. For service integration, apply Polly policies to external API calls, implement circuit breakers to prevent cascading failures, and define fallback behaviors. This ensures client applications can robustly handle integration failures.