对于未更改的静态内容，Amazon CloudFront不会一直返回304（未修改）？

A grid of EC2 web servers is running behind an ELB load balancer. The ELB is behind Amazon's CloudFront content delivery network. Content Delivery Networks are very new to me. My understanding is that CloudFront is supposed to speed up performance by caching static content at its "edges". But this isn't what's happening.A grid of EC2 web servers is running behind an