limit-concurrency-policy.md

title	description	services	author	ms.service	ms.topic	ms.date	ms.author
Azure API Management policy reference - limit-concurrency | Microsoft Docs	Reference for the limit-concurrency policy available for use in Azure API Management. Provides policy usage, settings, and examples.	api-management	dlepow	api-management	article	03/18/2024	danlep

Limit concurrency

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The limit-concurrency policy prevents enclosed policies from executing by more than the specified number of requests at any time. When that number is exceeded, new requests will fail immediately with the 429 Too Many Requests status code.

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Policy statement

<limit-concurrency key="expression" max-count="number">
        <!— nested policy statements -->
</limit-concurrency>

Attributes

Attribute	Description	Required	Default
key	A string. Specifies the concurrency scope. Can be shared by multiple policies. Policy expressions are allowed.	Yes	N/A
max-count	An integer. Specifies a maximum number of requests that are allowed to enter the policy. Policy expressions aren't allowed.	Yes	N/A

Usage

• Policy sections: inbound, outbound, backend, on-error
• Policy scopes: global, workspace, product, API, operation
• Gateways: classic, v2, consumption, self-hosted

Example

The following example demonstrates how to limit number of requests forwarded to a backend based on the value of a context variable.

<policies>
  <inbound>…</inbound>
  <backend>
    <limit-concurrency key="@((string)context.Variables["connectionId"])" max-count="3">
      <forward-request timeout="120"/>
    </limit-concurrency>
  </backend>
  <outbound>…</outbound>
</policies>

Related policies

• Rate limiting and quotas

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