web server responsiblity: manager resource, handle with tcp connection, itself administration
1. The request / response workflow:
An screenshot from firebug which measure the detail performance.
2. Proxy
Adding more than lay between client and server, it can do more things: filter, secuty, performance, cache.
Notes： trace can access this kind of proxies。
3. Cache
CDN http://en.wikipedia.org/wiki/Content_delivery_network
It need to sync, freshness check, and validation.
4. Integration Points: Gateways, Tunnels, and Relays
Gateways: webserver can communication with application with low performance.
Tunnels: You can send non-HTTP traffic through HTTP connections, allowing other protocols to piggyback on top of HTTP
