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Bellwether: Surrogate Services for Popular Content

Bellwether: Surrogate Services for Popular Content. Duane Wessels & Ted Hardie NANOG 19 June 12, 2000. The Slashdot Effect is a DDOS. “CNN Events” can: melt your network overwhelm servers dedicated to specific content prevent maintenance designed to fix the problem.

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Bellwether: Surrogate Services for Popular Content

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  1. Bellwether: Surrogate Services for Popular Content Duane Wessels & Ted Hardie NANOG 19 June 12, 2000

  2. The Slashdot Effect is a DDOS • “CNN Events” can: • melt your network • overwhelm servers dedicated to specific content • prevent maintenance designed to fix the problem. • This creates a denial of service for other content hosted on that network.

  3. A moving target is harder to hit. • A demand-driven surrogate located at the network border: • Moves the content away from low capacity networks. • Can handle the traffic for sites which experience sudden popularity. • Can help keep internal links uncongested

  4. What is a surrogate? surrogate: An intermediary program which acts as a server or tunnel for the purpose of responding to requests on behalf of one or more origin servers. Requests are serviced internally from a cache or by tunnelling them on to origin servers. Surrogates are also known as "reverse proxies" and "(origin) server accelerators". • Draft-ietf-wrec-taxonomy-03.txt

  5. No, really, what is a surrogate? • Proxies act on behalf of users; surrogates act on behalf of content providers. • A surrogate is any network element that acts on behalf of an origin server to respond to queries: • A mirror is a pre-populated surrogate. • A content delivery network (Akamai, Adero, Mirror Image) may provide surrogate services. • A demand-driven surrogate is a system activated only when popularity overloads an origin server or its network.

  6. Bellwether • Demand-driven surrogate based on • Squid • Zebra, • FreeBSD • IP firewall • GRE • And ideas stolen from CenterTrack.

  7. A picture is worth 1K words:

  8. Step 1: Administrative Setup • Configure a GRE tunnel from the surrogate to an internal router. • Configure the surrogate as a BGP peer of the border router. • Add origin hostnames to Squid access control list.

  9. Step 2: Activation • The surrogate injects a route to the popular origin server into border router’s BGP table. • The surrogate configures firewall rules to divert new HTTP connections to Squid. • Existing TCP connections and other traffic flow through GRE tunnel to the origin.

  10. Step 3: Operation • Squid creates a cache of popular content by forwarding requests to the origin server via the GRE tunnel and storing responses. • Cache hits are served from Squid, reducing the load on origin server and network alike.

  11. Simulation Workload • An origin server with a network bottleneck publishes suddenly popular content. • Client requests increase from 5 to 100 per second over 15 minutes. • Content remains popular for 2 hours, then trails off over 4 hours. • Target hit ratio is 90%. • Surrogate is PII/333 with 512 RAM and 2 SCSI disks.

  12. What if you need more? • For this result set, the surrogate is a dual PIII/550 Xeon with 2GB RAM and 10 SCSI disks. • Peak throughput is 475 HTTP requests per second. • Mean response size is 13KB. • About 45 Mbps of data flow.

  13. Next Steps • Improve error handling. • Handle overload by passing overflow traffic back to origin server. • Withdraw route in the event of Squid failure. • Use NECP to signal surrogate to start/stop service. • NECP daemon process and API • Prototype integration in Apache • Integration with higher layer switches.

  14. Final Questions • When you see a popularity spike, what melts? • What kinds of processes and devices need to activate a surrogate?

  15. Handy URLs: • To pick up a copy of bellwether: • ftp://ftp.equinix.com/bellwether • To discuss surrogate deployments: • surrogates-request@equinix.com • (Majordomo syntax) • Contact Ted or Duane: • hardie@equinix.com • wessels@packet-pushers.com

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