The underlying observation that shapes the structure of the API is that a high-performance API should adopt the lessons learned from the design of high-performance server architectures. As a result, we use an event-driven approach as the most basic interaction mechanism, exposing this level directly to modules as well as using it to construct support for additional communication models based on processes or threads. By exposing the event-driven structure directly to modules, the API can achieve high scalability with minimal performance impact on the proxy. This approach dispenses with multiple thread contexts or multiple processes, enabling the scalability gains previously observed for server software [13]. The rest of this section describes how the API integrates with HTTP processing in the cache and how customization modules are designed and invoked.