CS4262 Distributed Systems
Some slides extracted from Dr. Srinath Perera & Dr. Rajkumar Buyya’s
The Web – Simple on Outside…
…But Problematic on Inside
Browser takes a long time to load pages
Browser hangs, user needs to hit refresh
Streams are jerky
Browser connects but doesn’t fully load the page
Solution – Content Delivery Networks
at Network Edge
Content Delivery Networks (CDNs)
Through browser cache & proxies
If content is static, not much investment is needed from
Significant fraction of HTTP objects not cacheable
Need investment from content provider
Provider lacks of control & customization
Replicate content on a distribution network
Provider has control & customization
Low investment from content provider side
Conventional vs. CDN
How to replicate content?
Where to replicate content?
How to find replicated content?
How to choose among known replicas?
How to direct clients towards a replica?
CDN Options – HTTP Redirects
Origin server rewrites pages to serve content via CDN
10Page that distributes content via CDN
Traditional Web page on server
CDN Options – DNS Based
11A. Su, D. R. Choffnes, A. Kuzmanovic, & F. E. Bustamante, “Drafting behind Akamai (travelocity-
based detouring), “ ACM SIGCOMM Comput. Commun. Rev. 36, 4, Aug. 2006, pp. 435-446.
Application based (HTTP redirects)
Application-level, fine-grained control
Additional load & high RTTs, hard to cache
Naming based (DNS selection)
Well-suitable for caching, reduce RTTs
Request by resolver not client, request for domain not URL,
hidden load factor of resolver’s population