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1
Content Delivery Networks
iBAND2May 24, 1999
Dave FarberCTO
Sandpiper Networks, Inc. www.sandpiper.net
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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
rag
e re
sp
on
se
tim
e (
se
con
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