1. DotSlash An Automated Web Hotspot Rescue System Jonathan Bulava CSC8530 – Distributed Systems Dr. Paul Schragger

2. What is DotSlash?  An automated web hotspot rescue system.  Implementation is similar to Content Delivery Networks (CDN).  People: Weibin Zhao & Henning Schulzinne at Columbia University

3. Slashdot Effect  A term used when web servers cannot handle an influx of traffic due to links from more popular websites.  Bandwidth is consumed and/or the large number of requests cannot be processed.

4. Core Techniques  Detecting and predicting overload conditions in real time.  Discovering rescue servers in wide area networks.  Manage rescue relationships.  Designing and evaluating efficient mechanisms for replicating contents dynamically and redirecting client requests in wide area networks.

5. A Mutual-aid Community  Cost effective solution compared to CDN systems.  Spare capacity in the community is utilized to handle hotspots for an individual site.  Establishes a peer-to-peer communication model.

6. Configurations Configuration Bottlenecks Addressed Used By Dots_ApacheNetwork and web server Static/dynamic content web sites Dots_Apache + Dots_PHP Network, web server, and application server Dynamic content web sites Dots_Apache + Dots_PHP + Dots_MySQL Network, web server, application server, and database server Dynamic content web sites The prototype uses a LAMP configuration. Only Dots_Apache is required to use DotSlash.

7. Dots_Apache  An Apache module that supports basic DotSlash functions. Workload monitoring Rescue server discovery Rescue relationship management Request redirection Dynamic virtual hosting Dynamic DNS update

8. Dots_PHP  An extension for the PHP module that supports replicating PHP scripts dynamically. Dots_MySQL  A cache-enhanced data driver that supports caching database query results on demand.  Requires the memcached engine and libmemcache C library.

9. State Transitions and Restrictions NormalSOSRescue Complete release Initial allocation Additional allocation Partial release Accept rescue request Partial shutdown Accept rescue request Complete shutdown S1 S2 S8 S7 S4 S3 S4 S6 rescuing States are mutually exclusive i.e. a server cannot provide a rescue server while receiving a rescue service.

10. HTTP Request Rescue Client origin.com DNS rescue.com DNS www.origin.com (1.2.3.4) www.rescue.com (5.6.7.8) Cache DNS round-robin and Dynamic Virtual Hosting are implemented to manage rescue servers. (e.g. www-vh1.rescue.com, www-vh2.rescue.com, etc.)

11. Rescuing Dynamic Content  Original PHP (or other server-side script) is cached on rescue servers.  File Inclusions (include, require, etc.) Customized error handler for each script.  Security Issues? Client www.origin.com (So) www.rescue.com (Sr) DB (1) (2) (7) (6) (5) (4) (3) (8)

12. Effectiveness

13. The Database Bottleneck Client Database Server Query Result Cache Web/Application Server Data Driver Query Result Cache Web/Application Server Data Driver Original Server Rescue Server Database Server

14. References  Weibin Zhao, DotSlash,.  Weibin Zhao and Henning Schulzrinne, "Building an Adaptive Distributed Web Server System on the Fly for Handling Web Hotspots," in ACM Symposium on Principles of Distributed Computing (PODC'04) (brief announcement), St. John's, Newfoundland, Canada, July 2004.  Weibin Zhao and Henning Schulzrinne, "DotSlash: Handling Web Hotspots at Dynamic Content Web Sites," in IEEE Global Internet Symposium, Miami, Florida, March 2005.  “Slashdot effect.” Wikipedia.