Dellenny provides a hands-on guide to implementing the API Gateway pattern on Azure using API Management, explaining how to route, secure, and monitor requests to microservices for robust and maintainable architectures.

API Gateway Pattern in Azure: Managing APIs and Routing Requests to Microservices

Author: Dellenny

In microservices architectures, each service runs independently with its own database, introducing both flexibility and complexity. One major challenge is enabling clients to communicate securely and efficiently with these distributed services. The API Gateway pattern addresses this, and on Microsoft Azure, Azure API Management (APIM) is the preferred solution.

What is the API Gateway Pattern?

An API Gateway acts as a unified entry point for your microservices systems. Instead of clients calling many backend services directly, they communicate with the gateway, which handles:

  • Routing requests to the correct microservice
  • Transforming requests/responses as needed
  • Securing APIs with authentication (OAuth 2.0, JWT)
  • Aggregating data from multiple services

This makes the gateway the main security and operational interface to your APIs.

Why Use API Gateway on Azure?

Azure API Management provides a fully managed, feature-rich gateway with:

  • Central API management and control
  • Traffic management/throttling
  • Built-in security policies (OAuth 2.0, JWT, subscription keys)
  • Usage analytics with Azure Monitor
  • Payload transformation support (JSON ↔ XML)

APIM shields backend services from exposure and simplifies client integration.

How Does the API Gateway Pattern Work on Azure?

1. Clients Communicate with the Gateway

All application clients (web, mobile, partners) send their requests to the Azure APIM endpoint, not directly to backend services.

Example:

https://api.contoso.com/orders

2. Gateway Routes Requests

APIM uses configured policies to route requests to the right backend service.

Examples:

  • GET /orders → Orders microservice
  • POST /customers → Customer microservice

Clients remain unaware of backend endpoints, ports, or scaling concerns.

3. Policies Add Intelligence

Azure APIM policies (expressed in XML) can:

  • Manipulate inbound, backend, and outbound traffic
  • Set backend service URLs
  • Enforce authentication and authorization

Sample policy:

<inbound>
  <set-backend-service base-url="https://orders-service.azurewebsites.net" />
  <validate-jwt header-name="Authorization" failed-validation-httpcode="401" />
</inbound>

4. Security and Governance at the Gateway

Using APIM as your gateway lets you:

  • Apply OAuth 2.0 and JWT validation centrally
  • Enforce rate limiting (throttling)
  • Monitor all usage via Azure Monitor or Application Insights

Typical Architecture Flow

  1. Client Request → API Gateway (APIM)
  2. Policy Execution (auth, transformation, logging)
  3. Backend Routing
  4. Response Aggregation (optional)
  5. Unified Response to Client

Diagram:

[ Clients ] → [ Azure API Management ] → [ Microservices ]

Best Practices

  • Use versioned API paths (e.g., /v1/orders) to prevent breaking changes
  • Keep the gateway stateless; backend services hold persistent state
  • Set up monitoring and alerts (Azure Monitor, Application Insights)
  • Minimize transformation logic within APIM for better performance
  • Use caching for high-frequency endpoints

Conclusion

The API Gateway pattern, especially with Azure API Management, provides a secure, consistent, and manageable entry point for microservices. It simplifies maintenance, improves scalability, and enhances security by centralizing API exposure and policy enforcement.

If your microservices architecture is becoming overwhelming, adopting an API Gateway (like APIM) is like introducing a single point of contact—giving clients one clear way in, and you full control over how requests are handled.

This post appeared first on “Dellenny’s Blog”. Read the entire article here