Caching in APIM

• 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
• APIM has this feature built in caching mechanism
• You can also configure an external cache to work with an APIM
• Links:
  • https://docs.microsoft.com/en-us/azure/api-management/api-management-howto-cache
  • https://docs.microsoft.com/en-us/azure/api-management/api-management-caching-policies

Caching policies

• Response caching policies
  • Get from cache - Perform cache look up and return a valid cached responses when available.
  • Store to cache - Caches responses according to the specified cache control configuration.
• Value caching policies
  • Get value from cache - Retrieve a cached item by key.
  • Store value in cache - Store an item in the cache by key.
  • Remove value from cache - Remove an item in the cache by key.

Response caching

• Response caching is just one of the features
• Response caching means that when similar requests are called APIM will automatically respond without your back end ever getting hit thus saving load and bandwidth consumption
• How response caching works:
  • the unique request comes in and the inbound processor checks the cache to see if it has the response for that request
  • If not, your back end is called. Then, on the way back, the outbound processor stores that response data in the cache
  • The next time a request comes in, the inbound processor identifies that it has an existing response in the cache and it returns it, never calling your back end service

Configuring response caching

• Go to resource groups: https://portal.azure.com/#blade/HubsExtension/BrowseResourceGroups
• Select resource group > API Management service
• APIs section > APIs
• Select target API > Select All operations
• Click on ‘</>’ to open policy editor (either Inbound or outbount, both will open the same policy editor)
  • Add inbound and outbound policies
  • To make it work, both Inbound and Outbound policies need to be set
• Save

Inbound 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>

Outbound policy

<cache-store duration="20" />

Details: https://docs.microsoft.com/en-us/azure/api-management/api-management-howto-cache#-add-the-caching-policies