⚡ Example: Rate Limiting in Azure API Management

 

Scenario:

You have a public API and want to limit each user to 5 calls per minute to prevent abuse or accidental overload.

🛡️ What is Rate Limiting?

Rate limiting controls how many requests a client can make to your API within a specific time window.

It helps:

  • Prevent API abuse

  • Protect backend systems

  • Fairly distribute API usage

💡 Using the rate-limit-by-key Policy

Azure APIM uses a policy called rate-limit-by-key. It limits requests based on a unique identifier — usually the caller's subscription key or IP address.

🔧 Example Policy (XML)

Here’s how you can add this to your inbound policy:


<inbound>
  <base />
  <rate-limit-by-key 
      calls="5" 
      renewal-period="60" 
      counter-key="@(context.Subscription?.Key)" />
</inbound>

Explanation:

AttributeMeaning
calls="5"Maximum 5 calls allowed
renewal-period="60"Time window of 60 seconds (1 minute)
counter-keyUniquely tracks by subscription key (per user limit)

🚀 Where to Apply This

You can apply this policy at:

  • Product level (to all APIs in that product)

  • API level (to a specific API)

  • Operation level (for a specific endpoint)

⚠️ What Happens When the Limit is Hit?

When a caller exceeds the limit, APIM responds with:

  • HTTP 429 (Too Many Requests)

  • Optionally, include a custom error message or retry-after header

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