CSE 124 Lecture Notes - Lecture 25: Network Virtualization, Akamai Technologies, Hypertext Transfer Protocol
2 Jun 2018
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Web Caching
- many clients transfer the same information!
- generates redundant server and network “load”
- clients may experience high latency
WHY web caching?
- motivation for placing content closer to client!
- end users get better response time
- network gets “reduced” load
- why does caching work? Exploits locality of reference
- how well?
- up to a limit
- LARGE overlap in content
Caching w/ Reverse Proxies
- reverse proxies - located NEXT to origin servers
- “origin” (web) server - has content the user wants
- keep content in proxies
- clients go THROUGH proxies
- gives the “illusion” that client is talking to origin server
- does not work for dynamic content
How does a client get “redirected” to a proxy instead of the origin server?
- Rules “rewrite” requests to a proxy (covered in 123?)
Caching w/ Forward Proxies
- these type of proxies exist in home networks!
- your local IP (internet provider) has a local “proxy” that has the most popular content
- local client actually never communicated over the internet!
- you typically have to program your “browser” to know about the local proxy!
- designed to “eliminate” latency of having to go through the internet
Content-Distributed Networks
- forward proxies “start” with NO content
- accumulates content from users that is popular
- content changes based on user demand
-CDN: proactive content replication
- content provider “pushes” content out from its OWN origin server
- CDN replicates content on many servers
- updates are “pushed” to replicas when the content changes
Replica Selection: Goals
- requires continuous monitoring of “liveness, load, and performance”
- not a STATIC optimization! Network performance is HIGHLY variable!
Document Summary
Motivation for placing content closer to client! Reverse proxies - located next to origin servers. Origin (web) server - has content the user wants. Gives the illusion that client is talking to origin server. Rules rewrite requests to a proxy (covered in 123?) These type of proxies exist in home networks! Your local ip (internet provider) has a local proxy that has the most popular content. Local client actually never communicated over the internet! You typically have to program your browser to know about the local proxy! Designed to eliminate latency of having to go through the internet. Accumulates content from users that is popular. Content provider pushes content out from its own origin server. Updates are pushed to replicas when the content changes. Requires continuous monitoring of liveness, load, and performance . ~100,000 servers ( forward proxies ) in 70 countries worldwide! About 20 million client requests per second.
