1. Handling Web Hotspots at Dynamic Content Web Sites Using DotSlash Weibin Zhao Henning Schulzrinne {zwb,hgs}@cs.columbia.edu Columbia University NYMAN’04 September 10, 2004

2. 09/10/2004 DotSlash2 The Problem Web hotspots Short-term dramatic surge of request rate Flash crowds, the Slashdot effect Dynamic content web sites CPU-bound, request rate supported is low Hard to cache dynamic content Bottleneck at different servers On-line bookstore (Amazon): database Auction (eBay), bulletin board (Slashdot): web

3. 09/10/2004 DotSlash3 Our Approach DotSlash Rescue system M utual aid, spare capacity, cost effective Self-configuring, fully automated Build an adaptive distributed web server system on the fly Scalable, easy to use, transparent to clients DotSlash for dynamic content Remove the web server bottleneck Dynamic script replication

4. 09/10/2004 DotSlash4 DotSlash Overview Components Workload monitoring: CPU/Link Rescue server discovery: different sites Load migration: HTTP redirect, DNS-RR Dynamic virtual hosting: on the fly Adaptive rescue control: desired load region Implementation LAMP: Apache module, PHP extension Dynamic DNS: dot-slash.net Service discovery: enhanced SLP

5. 09/10/2004 DotSlash5 Rescue Examples originrescue DNS (1) (2) (1) (2) (3) origin serverdatabase rescue server MySQLApache PHP (1) (2) (3) reverse proxy Static content Load migration: HTTP redirect Replicate scripts dynamically Dynamic content DNS round-robin

6. 09/10/2004 DotSlash6 Dynamic Script Replication Operations at rescue server Map a redirected URI to a script file Trigger 404 handler if the script file not found Retrieve the script file Handle file inclusions Set query variables Run the script by invoking native include Operations at origin server If a request is from a rescue server and for dynamic content, return the script file

7. 09/10/2004 DotSlash7 Handling File Inclusions The problem A replicated script may include files that are located at the origin server Assume: included files under DocumentRoot Approaches Renaming inclusion statements Need to parse scripts: heavy weight Customized error handler Catch inclusion errors: light weight

8. 09/10/2004 DotSlash8 Evaluation Experimental Setup Linux machines: HC, LC Apache: 2.0.49, DotSlash module PHP: 4.3.6, DotSlash extension MySQL: 4.0.18, open_files_limit, max_connection RUBBoS bulletin board benchmark 19 scripts: 1 KB to 7 KB 439 MB database

9. 09/10/2004 DotSlash9 R: max request rate supported No rescue: R=118With rescue: R=245 #rescue servers: 9 Origin (HC)DB (HC) Rescue (LC) Configuration: Rescue (LC) 245/118>2 CPU: Origin=100%, DB=45%

10. 09/10/2004 DotSlash10 Effectiveness No rescue: R=49 With rescue: R=245 245/49=5 origin serverHCLC improvement25 #rescue servers910 Conclusion: remove web server bottleneck Origin (LC) DB (HC) Rescue (LC) Another Configuration: Comparison: #rescue server: 10 Rescue (LC)

11. 09/10/2004 DotSlash11 CPU Utilization Control

12. 09/10/2004 DotSlash12 Workload Migration

13. 09/10/2004 DotSlash13 Handling Worst-Case Workload Settling time: 24 second #timeouts 921/113565

14. 09/10/2004 DotSlash14 Settling Time vs. #Timeouts Assign different priorities to rescue requests and client requests Allocate rescue servers in parallel

15. 09/10/2004 DotSlash15 Conclusions Prototype 10-fold improvement for static content web sites Removing the web server bottleneck for dynamic content web sites On-going work DNS-RR experiments PlanetLab experiments for dynamic content Real Slashdot test For further information http://www.cs.columbia.edu/IRT/dotslash