1. DotSlash: An Automated Web Hotspot Rescue System
Weibin Zhao
Henning Schulzrinne
Department of Computer Science
Columbia University

2. The Problem Web hotspots Existing mechanisms are not sufficient
Also known as flash crowds, the Slashdot effect
Short-term dramatic load spikes at web servers
Existing mechanisms are not sufficient
Over-provisioning
Inefficient for rare events
Difficult because the peak load is hard to predict
CDNs
Expensive for small web sites that experience the Slashdot effect
DotSlash
12/7/2018

3. The Challenges Automate hotspot handling
Eliminate human intervention to react quickly
Improve availability during critical periods (15 minutes of fame)
Allocate resources dynamically
Static configuration is insufficient for unexpected dramatic load spikes
Address different bottlenecks
Access network, web server, application server, and database server
DotSlash
12/7/2018

4. Our Approach DotSlash Advantages
An automated web hotspot rescue system by building an adaptive distributed web server system on the fly
Advantages
Self-configuring
Service discovery, adaptive control, dynamic virtual hosting
Scalable, easy to use, and transparent to clients
DotSlash
12/7/2018

5. DotSlash Overview Rescue model DotSlash components
Mutual aid community using spare capacity
Potential usage by web hosting companies
DotSlash components
Workload monitoring
Rescue server discovery
Load migration (request redirection)
Dynamic virtual hosting
Adaptive rescue and overload control
DotSlash
12/7/2018

6. Handling Load Spikes Request redirection Handle different bottlenecks
DNS-RR: reduce arrival rate
HTTP redirect: increase service rate
Handle different bottlenecks
Technique
Bottleneck Addressed
Cache static content
Network, web server
Replicate scripts dynamically
Application server
Cache query results on demand
Database server
DotSlash
12/7/2018

7. Rescue Example Cache static content client1 origin server
(2) HTTP redirect
(4)
(3)
(1)
reverse proxy
origin server
rescue server
(3)
(4)
(1)
client2
DNS server
(2)
DNS round robin
DotSlash
12/7/2018

8. Rescue Example (2) Replicate scripts dynamically origin server
Apache
origin server
PHP
database
server
(1)
(6) PHP
client
(2)
(5) PHP
(4)
(3)
(7)
rescue server
(8)
MySQL
Apache
DotSlash
12/7/2018

9. Rescue Example (3) Cache query results on demand database origin
server
query result cache
origin
server
client
data driver
database
server
query result cache
rescue
server
data driver
DotSlash
12/7/2018

10. Allocate rescue server
Server States
Origin server
Get help from others
SOS state
Allocate rescue server
Release all rescues
Normal state
Accept SOS request
Shutdown all rescues
Rescue server
Provide help to others
Rescue state
DotSlash
12/7/2018

11. Adaptive Overload Control
Objective
CPU/network in desired load region
Origin server
Allocate/release rescue servers
Adjust redirect probability
Rescue server
Accept SOS requests
Shutdown rescues
Adjust allowed redirect rate
DotSlash
12/7/2018

12. Implementation Based on LAMP (Linux, Apache, MySQL, PHP)
Apache module (mod_dots), DotSlash daemon (dotsd), DotSlash rescue protocol (DSRP)
Dynamic DNS using BIND with dot-slash.net
Service discovery using enhanced SLP
Apache
mod_dots
SHM
dotsd
other
dotsd
DSRP
HTTP
client
SLP
DNS
BIND
mSLP
DotSlash
12/7/2018

13. Evaluation Workload generation Testbed Metrics
httperf for static content
RUBBoS (bulletin board) for dynamic content
Testbed
LAN cluster and WAN (PlanetLab) nodes
Linux Redhat 9.0, Apache , MySQL , PHP 4.3.6
Metrics
Max request rate and max data rate supported
DotSlash
12/7/2018

14. Performance Static content (httperf) Dynamic content (RUBBoS)
10-fold improvement
Relieve network and web server bottlenecks
Dynamic content (RUBBoS)
Completely remove web/application server bottleneck
Relieve database server bottleneck
Overall improvement: 10 times for read-only mix, 5 times for submission mix
DotSlash
12/7/2018

15. Conclusions DotSlash prototype On-going work For further information
Applicable to both static and dynamic content
Promising performance improvement
On-going work
Address security issues in deployment
Release DotSlash as open source software
For further information
DotSlash framework: WCW 2004
Dynamic script replication: Global Internet 2005
On-demand query result cache: TR CUCS (under submission)
DotSlash
12/7/2018