WebQ

Servers often crash when faced with transient overload, causing user experience to degrade sharply when incoming load exceeds capacity. Existing overload control mechanisms focus on some form of admission control to protect the web server from overload. Importantly, there is no feedback to the frustrated user about when to retry again, leading to adhoc retries.

WebQ consist of two web proxies, that together simulate a virtual queue of web requests, and shape incoming load to match server capacity. Users accessing a server protected by WebQ receive a HTTP redirect response specifying a wait time in the virtual queue, and are automatically redirected to the web server upon expiration of the wait time. The wait times are calculated using an estimate of the server’s capacity that is computed by WebQ. Users in the virtual queue are provided with a secure cryptographic token, which is checked to guarantee that the user has waited his prescribed time in the queue.

Directory Structure

• bin - Scripts to deploy all the components.
• TokenCheck - Source code and documentation of Token Check.
• TokenGen - Source code and documentation of Token Gen.
• ServerScripts - Scripts and details on how to setup a test Moodle server.
• CapacityEstimator - Source code and documentation of Capacity Estimator.
• JMeter_test_configurations - Test configuration used when testing with jmeter [deprecated]. Use LoadGenerator instead.

Developer Manual

Please find the document developer_manual.pdf under the doc folder of respective folders. It contains detailed instructions for understanding the codebase. It will be helpful while modifying/adding code functionalities to WebQ.

Configuration and Machine Setup

redeploy.sh script at bin/ is used to bring up all the components in different machines. Before redeploy.sh can be successfully run some configurations have to done on respective machines running the components.

1. Clone this repo in each of the machines. One machine may run multiple components. for e.g: TokenGen and CapacityEstimator and run at one machine and that machine can run redeploy.sh as well.
2. Chose one machine as a PRIMARY machine and grant password-less root access to all other machines. This machine is will run redeploy.sh.
3. At TokenGen machines update proxy.conf with correct TokenCheck ip.
4. At TokenCheck configure lighttpd.conf with correct proxy server ip. Configure CapacityEstimator ip in btp.h. Make and build TokenCheck.(Detailed configuration and build instructions available in TokenCheck/README.md).
5. At CapacityEstimator install Matlab and java. Configure webq.properties file with correct TokenGen ip and port.
6. At TestServer setup Test Moodle. Install test scripts available at ServerScripts (See ServerScripts README).
7. Run redeploy.sh from PRIMARY machine to start using WebQ for TestServer.

Publications

• WebQ: A Virtual Queue To Improve User Experience During Web Server Overload
  Bhavin Doshi, Chandan Kumar, Pulkit Piyush, Mythili Vutukuru
  IEEE/ACM International Symposium on Quality of Service (IWQoS), Portland, OR, June 2015.