1. DotSlash – A Web Hotspot Rescue System Weibin Zhao Henning Schulzrinne Department of Computer Science Columbia University June 11, 2004

2. 06/11/04 DotSlash2 The Problem Web hotspots A short-term sudden, dramatic surge of request rate “15 minutes of fame” Existing mechanisms Capacity planning Content delivery networks (CDNs) Caching Admission control

3. 06/11/04 DotSlash3 DotSlash A hotspot rescue system mutual-aid community, use spare capacity Self-configuring, adaptive, scalable server directory mutual-aid community server

4. 06/11/04 DotSlash4 DotSlash Components Workload monitoring Rescue server discovery Load migration: HTTP redirect, DNS-RR Dynamic replication and caching Rescue control originrescue DNS (1) (2) (1) (2) (3)

5. 06/11/04 DotSlash5 increasing throughput Handling Load Spikes origin rescue origin reducing arrival rate: DNS-RR increasing service rate: HTTP redirect

6. 06/11/04 DotSlash6 Benefit of Using HTTP Redirect Reducing network load Caching static content Reducing CPU load Replicating scripts dynamically origin server database rescue server PHP MySQL Apache PHP web server is the bottleneck, not database server (1) (2) (3)

7. 06/11/04 DotSlash7 Server Status Normal Rescue SOS AllocateRelease Accept SOSShutdown Origin server Getting help from others Rescue server Providing help to others

8. 06/11/04 DotSlash8 Workload Regions heavily loaded region lightly loaded region desired load region upper threshold lower threshold reference load 0 100% 70% 50% 60%

9. 06/11/04 DotSlash9 Rescue Control Objective CPU/Link in the desired load region Origin server Rescue serve allocation/release Adjusting redirect probability Rescue server Accept SOS, shutdown rescue Adjust allowed redirect (data) rate

10. 06/11/04 DotSlash10 Origin Server Workload monitoring HTTP redirect Use rescue server aliases Don’t redirect requests from rescue servers Redirect Policies: WRR DNS round-robin Add/remove rescue server IP addresses

11. 06/11/04 DotSlash11 Rescue Server Workload monitoring Reverse caching proxy Caching: concurrency control Different requests A regular request A reverse proxy request to origin server (active rescue) An HTTP redirect to origin server (expired rescue) Dynamic DNS update Register new aliases

12. 06/11/04 DotSlash12 Implementation LAMP: Apache, PHP, MySQL Dynamic DNS: dot-slash.net Service discovery: enhanced SLP Workload: httperf, RUBBoS Testing: LAN and PlanetLab BINDmSLP HTTP SHM SLP DNS DSRP Other Dotsd Client Apache Dotsd Mod_dots

13. 06/11/04 DotSlash13 Conclusion Preliminary version implemented Measurement: 10-fold improvement Adaptive overload control On-going work Evaluation Dynamic content DNS-RR Real Slashdot test Software distribution