About Purge Cache

This document discusses the interfaces used to purge the cache that is used to store static objects at the edge. Purging cache is done to refresh static content.

When you serve content through the edge network, one significant benefit is the ability to cache content at the “edge” of the Internet, that is, near the end user. The normal method to refresh or replace the content is to set a TTL (time-to-live) in cache for objects, which you can set by way of max-age type response headers or by configuration files.

When the TTL expires, a server receiving a client request checks with the origin using a conditional HTTP GET (also called an If-Modified-Since, or IMS, GET request). If the object has changed, the origin server sends the new version; otherwise, the origin sends an HTTP 304 Not Modified response, and the edge server serves the cached instance of the object. Numerous options and variations on this scenario are provided, but that is the basic mechanism.

When you need to manually refresh the content and not wait for TTL expiration, two basic mechanisms are provided to meet different needs and preferences, and the basic mechanisms have a variety of interfaces you can use:

  • Fast Purge—allows you to specify objects by Uniform Resource Locators (URL) with Akamai Cache Keys (ARL), CP codes or Cache Tags to remove from cache and refresh from the origin. Fast Purge can be used as a web interface in the Control Center and as a REST API. For documentation, see Fast Purge API.
  • Enhanced Content Control Utility (ECCU)—allows you to specify objects to refresh by rules using path and extensions or other, more complex criteria. ECCU can be used as a web interface in the Control Center and as a REST API. For documentation, see Enhanced Content Control Utility API.
    • Using the web interface, you can specify paths or extension rules directly. Or you can specifcy a file to upload with more complex rules by which objects will be refreshed, not only by path or extension, but also by the request header or method, protocol, or other criteria.
    • Using the ECCU API you can specify those same complex rules in the JSON request.