Design Patterns in C#
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Tutorials Design Patterns in C#

API Gateway Pattern — Complete Guide

API Gateway Pattern — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of Design Patterns in C# on Toolliyo Academy.

8 min read Updated 8/22/2026
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Design Patterns in C# · Lesson 45 of 69

API Gateway Pattern

GoF Core ✓ → Enterprise ✓ → Cloud & Craft

Cloud & Craft · 3 — Microservices & interviews · ~6 min · Module 6: Microservices & Cloud Patterns

What is this?

API Gateway is the single external entry for many services — routing, auth, rate limits, and request shaping.

Why should you care?

ShopNest mobile should not know twenty internal URLs and auth schemes.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

// Gateway routes
// /catalog/** -> catalog service
// /orders/**  -> order service
// cross-cutting: JWT validate, rate limit, request id
Console.WriteLine("GET /orders/1 -> OrderService");
Console.WriteLine("401 if JWT missing");

What happened?

  • Edge policies live at the gateway; domain logic stays in services.
  • Avoid turning the gateway into a business orchestrator.

Practice next

  1. Map three ShopNest routes.
  2. Validate JWT at gateway.
  3. Add rate limits on /pay.
  4. Separate admin gateway.
  5. Path rewrite for legacy clients.

Remember

Single front door. Policy at edge. Thin routing.

ShopNest public gateway

Apps call one base URL; gateway routes.

Outcome: Internal services stay private.

Interview prep for this lesson

Practice these questions aloud after reading—each links to a full structured answer.

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Abstract Expression (IExpression):?
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Design Patterns in C#
Course syllabus

Design Patterns in C# Tutorial

Module 1: Creational Design Patterns
Module 2: Structural Design Patterns
Module 3: Behavioral Design Patterns
Module 4: Enterprise Design Patterns
Module 5: Modern Enterprise Patterns
Module 6: Microservices & Cloud Patterns
Module 7: ASP.NET Core Architecture Patterns
Module 8: Interview & System Design
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