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limit-concurrency-policy.md

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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
azure-api-management
reference
07/23/2024
danlep

Limit concurrency

[!INCLUDE api-management-availability-all-tiers]

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.

[!INCLUDE api-management-rate-limit-accuracy]

[!INCLUDE api-management-policy-generic-alert]

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

Usage notes

  • The maximum number of requests enforced by API Management is lower when multiple capacity units are deployed in a region.

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

[!INCLUDE api-management-policy-ref-next-steps]