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Content Delivery Networks

iBAND2May 24, 1999

Dave FarberCTO

Sandpiper Networks, Inc. www.sandpiper.net

dave@sandpiper.net

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A popular web site

Browsers

Web Server

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Congestion slows delivery

Browsers

Web Servers

Routers

Networks

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• Reduces load on server• Avoids network congestion

Replicating content closer to users

Browsers

Web Server

Replicatedcontent

Router

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Content Delivery Networks

• Outsourcing for web publishers– lets existing web sites scale – serves content closer to end users– uses a massive, shared infrastructure– provides reserved resources– serves all clients

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Benefits for Web Publishers

• Improves quality of service• Scales easily as demand grows• Offers full-service management• Reduces costs

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The Footprint Network

• Content Distributors– replicate content– manage shared resources

• Content Migrators– determine when to

migrate requests– select the best distributor– rewrite HTML– provide publisher control

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The Footprint Network

• Improves connection to user– bandwidth is monitored for quality– distributors are located near clients– measurements identify the best distributor

• Allows capacity to scale– bandwidth can be increased quickly– new distributors can be added easily

• Works for ISPs– distributors reduce ISP peering costs– distributors cooperate with ISP caches

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Content Distributors

• Strategy– cache HTTP and FTP resources– adjust cache-control directives– publish updates by explicit

broadcasting of invalidations,and expiration policy

– collect and merges logs

• Results– very high hit rates– avoids control problems

created by traditional caches

Origin Server

ContentDistributor

Content Migrator

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Rendezvous: Migrator

• Strategy– operator specifies which

resources should “migrate”– migrator makes selection

as resources are served– URLs in HTML are rewritten

• Results– easy to deploy– most resources migrate

to distributor network– rewriting HTML reduces

visits to origin server and allows FTP redirection

Content Migrator

OriginServer

RuleBase

HTMLRewriter

HTTPRequest

HTTPReply

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Rendezvous: DNS

• Strategy– URLs in HTML are

modified before serving to use “supernames”

– browser uses DNS to resolve the supernameto a content distributor

– Sandpiper custom DNS servers resolve the nameto the best distributor

• Results– high scalability for very

busy web servers

OriginServer

HTMLRewriter

Browser

FootprintDNS server

ContentDistributor

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• Adapts to traffic conditions

• Supports a wide variety of content– static files - images, downloads, HTML – authenticated content– dynamic (custom) content– audio/video streaming

• Provides publisher controls– access to logs– complete control of content freshness

– coupled with client-side caches

Unique Footprint Services

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Selecting Best Distributor

• Strategy– group client IP addresses – measure network

congestion regularly– measure load frequently– use load and congestion data

to select best distributor

• Results– reduces delays

when net is congested– wide area load balancing– high availability of servers

Client IP address

Network map

Distributor load

Best Distributor Selection

Network status

Specific Content

Distributor

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Commercial Web Server Site

Ave

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ds)

Origin Server

With Footprint

Footprint Performance

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Serving HTMLfrom content distributors

• Many sites serve 50% or more HTML• Benefits

– increases scalability– improves performance

• Challenges– bookmarks on resources– cookies and authenticated content– customized dynamic content

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Custom domain names

• Distributor aliases for web publishers– http://38.200.111.132 /www.hotstuff.com/products– http://www41.hotstuff.com /products

• Benefits– name recognition value in each URL– bookmarks remain under publisher’s control– browsers send cookies and passwords to distributors– Java sandbox can talk to content distributors

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Cookies and Authentication

• Cookie support– custom domain names make cookies available– cookies are logged on receipt– cookies are forwarded when

custom content is required

• Authentication support– custom domain names make passwords available– requests are forwarded for authorization– content is cached & served by content distributor

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Custom content

• Dynamic content is customized per user• Many custom pages built from common elements

– ad insertions– custom home pages– product status updates

• Distributor-Side Include– origin server provides minimal custom content– Content Distributor assembles elements

OriginServer

ContentDistributor

Browser

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Streaming in Footprint

• Scales to vast numbers of viewers– without requiring changes to server

• Rendezvous clients with best server– using Sandpiper’s proprietary technology

• Replicates streams on demand– live via Real proxy (splitter)– on-demand via Inktomi’s Media Cache Option

• Uses existing shared infrastructure

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Footprint StreamingArchitecture

Browser Content Migrator Real G2

Server

Content Distributor

Origin Server

Inktomi TS/MCO

RealProxy

FootprintRequest Processor

rendezvous

cache fills &live streams

Browser

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Footprint offerspublisher-friendly caching

• Content distributors:– provide activity logs– keep resources “fresh”– guarantee local bandwidth– guarantee local disk space– handle more than HTTP traffic– give publishers control

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Coupling Footprintwith ISP caches

• Used by caching ISPs – for example, AOL

• Gives Footprint customers– access to logs– control of freshness

Browser

ISP Caches

ContentDistributor

OriginServer

ISP Network

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Working for ISPs

• For Demand-side ISPs, Footprint– reduces bandwidth costs– improves end user performance– couples with traditional caches– provides publisher-friendly caching– can serve browsers located anywhere

• For Supply-side ISPs, Footprint– extends ISP hosting services– offers differentiated services– increases the “reach” of your web publishers– provides additional source of revenue

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Conclusion

• Scaling Internet servers requires serving content closer to users

• Content Delivery Networks give publishers a way to scale

• Sandpiper’s Footprint provides a comprehensive set of benefits today

• Content Delivery Networks will become a natural part of the Internet infrastructure