13-MidtermReview - Midterm Review EE122 Fall 2011 Scott...

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1 Midterm Review EE122 Fall 2011 Scott Shenker http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks to Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley
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Announcements • Available after class • I hate these review lectures…. 2
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Agenda • Finish Web caching • Midterm review 3
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Finishing Up Web Caching 4
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5 Improving HTTP Performance: Caching • Many clients transfer same information – Generates redundant server and network load – Clients experience unnecessary latency Server Clients Backbone ISP ISP-1 ISP-2
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6 Improving HTTP Performance: Caching: How • Response header: Expires – how long it’s safe to cache the resource No-cache – ignore all caches; always get resource directly from server • If entry has not expired, cache returns it – Otherwise, it issues an if-modified-since • Modifier to GET requests: If-modified-since – returns “not modified” if resource not modified since specified time
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7 Improving HTTP Performance: Caching: Why • Motive for placing content closer to client: – User gets better response time – Content providers get happier users o Time is money, really! – Network gets reduced load • How well does caching work? – Very well, up to a limit – Large overlap in content – But many unique requests sound familiar?
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8 Improving HTTP Performance: Caching with Reverse Proxies Cache documents close to server b decrease server load • Typically done by content providers • Only works for static content Clients Backbone ISP ISP-1 ISP-2 Server Reverse proxies
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9 Improving HTTP Performance: Caching with Forward Proxies Cache documents close to clients b reduce network traffic and decrease latency • Typically done by ISPs or corporate LANs Clients Backbone ISP ISP-1 ISP-2 Server Reverse proxies Forward proxies
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10 Improving HTTP Performance: Caching w/ Content Distribution Networks • Integrate forward and reverse caching functionality – One overlay network (usually) administered by one entity e.g., Akamai • Provide document caching Pull: Direct result of clients’ requests Push: Expectation of high access rate • Also do some processing – Handle dynamic web pages Transcoding
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11 Improving HTTP Performance: Caching with CDNs (cont.) Clients ISP-1 Server Forward proxies Backbone ISP ISP-2 CDN
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12 Improving HTTP Performance: CDN Example – Akamai • Akamai creates new domain names for each client content provider. – e.g., a128.g.akamai.net • The CDN’s DNS servers are authoritative for the new domains • The client content provider modifies its content so that embedded URLs reference the new domains. – “Akamaize” content – e.g.: http://www.cnn.com/image-of-the-day.gif becomes http://a128.g.akamai.net/image-of-the-day.gif Requests now sent to CDN’s infrastructure…
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13 Hosting: Multiple Sites Per Machine • Multiple Web sites on a single machine – Hosting company runs the Web server on behalf of
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This note was uploaded on 01/09/2012 for the course ELECTRICAL 122 taught by Professor Shenker during the Spring '11 term at Berkeley.

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13-MidtermReview - Midterm Review EE122 Fall 2011 Scott...

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