API Gateway Patterns in .NET Core and Azure

This article is part of the Comprehensive Guide to Microservices Architecture in .NET Core, Cloud and Azure series. API gateways serve as the entry point for client applications in distributed architectures, handling request routing, composition, and protocol translation. As systems grow more complex with multiple client types and backend services, choosing the right gateway pattern becomes crucial for maintaining performance, scalability, and developer productivity. This article explores two powerful API gateway patterns in .NET: the Backend for Frontend (BFF) pattern, which creates client-specific gateways, and GraphQL, which offers flexible, query-driven data fetching. Both patterns address the challenge of efficiently serving diverse clients while maintaining clean architecture and optimal performance. Backend for Frontend (BFF) Pattern Web BFF Implementation The web BFF returns detailed, enriched data suitable for desktop browsers with higher bandwidth and processing power: [ ApiController ] [ Route ( "api/web/[controller]" )] public class OrdersController : ControllerBase { private readonly IOrderServiceClient _orderClient ; private readonly ICustomerServiceClient _customerClient ; private readonly IInventoryServiceClient _inventoryClient ; [ HttpGet ( "{id}" )] public async Task < WebOrderDto > GetOrder ( Guid id ) { // Execute parallel calls to improve response time var orderTask = _orderClient . GetOrderAsync ( id ); var customerTask = _customerClient . GetCustomerAsync ( id ); var inventoryTask = _inventoryClient . GetInventoryStatusAsync ( id ); await Task . WhenAll ( orderTask , customerTask , inventoryTask ); return new WebOrderDto { Order = orderTask . Result , Customer = customerTask . Result , InventoryStatus = inventoryTask . Result , // Include additional rich data for enhanced web UI experience RecommendedProducts = await GetRecommendationsAsync ( id ) }; } } Mobile BFF Implementation The mobile BFF provides optimized, lightweight responses to min