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Add caching to improve performance in Azure API Management

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APIs and operations in API Management can be configured with response caching. Response caching can significantly reduce latency for API callers and backend load for API providers. This article describes how to add caching to your APIs.

Important

Built-in cache is volatile and is shared by all units in the same region in the same API Management instance. Regardless of the cache type used (internal or external), if cache-related operations fail to connect to the cache because of the volatility of the cache or for any other reason, the API call that uses the cache-related operation doesn't raise an error, and the cache operation completes successfully. In the case of a read operation, a null value is returned to the calling policy expression. Your policy code should be designed to ensure that there's a fallback mechanism to retrieve data that's not found in the cache.

For more detailed information about caching, see API Management caching policies and Custom caching in Azure API Management.

Screenshot that shows cache policies in API Management.

In this article you:

  • Add response caching for your API
  • Verify that caching is working

Note

Internal caching isn't available in the Consumption tier of Azure API Management. You can use an external Azure Cache for Redis instead. You can also configure an external cache in other API Management service tiers.

Prerequisites

Add caching policies

With the caching policies shown in this example, the first request to a test operation returns a response from the backend service. This response is cached, keyed by the specified headers and query string parameters. Subsequent calls to the operation, with matching parameters, will return the cached response until the cache duration interval expires.

  1. Sign in to the Azure portal.

  2. Go to your API Management instance.

  3. Select APIs > APIs in the menu on the left.

  4. Select an API for which you want to configure caching.

  5. At the top of the screen, select the Design tab.

  6. In the Inbound processing section, select the </> icon:

    Screenshot that shows API Management APIs in the portal.

  7. In the inbound element, add the following policy:

    <cache-lookup vary-by-developer="false" vary-by-developer-groups="false">
    <vary-by-header>Accept</vary-by-header>
    <vary-by-header>Accept-Charset</vary-by-header>
    <vary-by-header>Authorization</vary-by-header>
</cache-lookup>

  8. In the outbound element, add the following policy:

    <cache-store duration="20" />

    In this policy, duration specifies the expiration interval of the cached responses. The interval is 20 seconds.

  9. Select Save.

Tip

If you're using an external cache, as described in Use an external Azure Cache for Redis in Azure API Management, you might want to specify the caching-type attribute of the caching policies. See API Management caching policies for more information.

Call an operation to test the caching

To test caching, call an operation in the portal.

  1. In the Azure portal, go to your API Management instance.
  2. Select APIs > APIs in the menu on the left.
  3. Select the API to which you added caching policies.
  4. Select an operation to test.
  5. Select the Test tab at the top of the window.
  6. Select Trace two or three times in quick succession.
  7. Under HTTP response, select the Trace tab.
  8. Jump to the Inbound section and scroll to the cache-lookup policy. You should see a message similar to the one in the following screenshot, which indicates a cache hit: Screenshot of cache-lookup when testing an API in the portal.

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