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Azure API Management (APIM)

Overview

Azure API Management (APIM) is a fully managed service in Azure that acts as a gateway between clients and your backend services or APIs.

It allows you to publish, secure, transform, monitor, and manage APIs in a scalable and consistent way — whether those APIs are hosted in Azure, on-premises, or elsewhere.

Think of it as a proxy layer that gives you control over how your APIs are consumed without changing the APIs themselves.

Core Components

  1. API Gateway – Accepts requests, applies policies (e.g., authentication, rate limiting), and forwards them to the backend.
  2. Publisher Portal (Azure Portal) – Where API developers manage APIs, configure policies, view analytics, etc.
  3. Developer Portal – A customizable, automatically generated site where API consumers can explore and test APIs.
  4. Policies – XML-based rules you apply to control behaviour, e.g., caching, transformation, validation.

Advantages

  • Centralized control – One place to manage all APIs across microservices, apps, or environments.
  • Security – Supports OAuth 2.0, JWT, IP filtering, rate limiting, and more.
  • Rate limiting & throttling – Prevent abuse and control traffic loads.
  • Monitoring & analytics – Built-in dashboard for usage, health, errors.
  • Versioning – Easily expose multiple versions of the same API.
  • Transformation – Modify requests/responses (e.g., XML ↔ JSON, renaming fields).
  • Caching – Reduce load on backend APIs with response caching.
  • Multi-region support – High availability and low latency for global applications.

Drawbacks / Considerations

  • Cost – Pricing tiers vary significantly; developer tier is cheap, premium is expensive (enterprise-grade).
  • Complexity – Configuring policies and versioning can become intricate.
  • Latency – Adds a small layer of processing time to requests.
  • Policy management – XML format for policies can be verbose and error-prone.

When to Use It

  • You have multiple APIs (internal or external) and want to control access consistently.
  • You’re exposing APIs to third parties or external clients.
  • You want to apply cross-cutting concerns like logging, auth, throttling, or transformation without changing code.
  • You need a developer portal or self-service onboarding for API consumers.

Example (C# API + APIM)

Let’s say you have a .NET Core Web API for a retail system:

[ApiController]
[Route("api/[controller]")]
public class OrdersController : ControllerBase
{
    [HttpGet("{id}")]
    public IActionResult GetOrder(int id)
    {
        return Ok(new { Id = id, Product = "Shirt", Quantity = 1 });
    }
}

After publishing this API to Azure App Service, you import it into APIM. Then:

  • Apply rate limiting (e.g., 100 requests per minute).
  • Require subscription keys (or OAuth).
  • Add a policy to change the response format or rename properties.

Example policy (XML) to rename fields in the response:

<inbound />
<backend />
<outbound>
  <set-body template="liquid">
    {
      "order_id": "{{body.Id}}",
      "item": "{{body.Product}}",
      "qty": "{{body.Quantity}}"
    }
  </set-body>
</outbound>

Monitoring Example

You get insights like:

  • Which endpoints are hit most?
  • Who are the top consumers?
  • What’s the average response time?
  • How many requests were blocked due to throttling?

Conceptual Model

Imagine you’re building a public-facing API platform:

  • Your developers write APIs in .NET or Java.
  • Your APIM enforces rate limits and security, and exposes the API docs via the Developer Portal.
  • You can manage the whole lifecycle of your APIs (versioning, deprecation, monitoring) without changing your codebase.