This project contains source code associated to the following article submitted to SRDS2014:

Cristian Klein, Alessandro Vittorio Papadopoulos, Manfred Dellkrantz, Jonas Dürango, Martina Maggio, Karl-Erik Årzén, Francisco Hernández-Rodriguez, Erik Elmroth "Improving Cloud Service Resilience using Brownout-Aware Load-Balancing"

Brownout is a software engineering paradigm to make cloud services more robust to capacity shortages. It requires the developer to mark a part of the response as optional and only serve it with a probability given by an external parameter, called the dimmer. A controller monitors the response time of the service and adjusts the dimmer, so as to keep the application responsive. Details can be found in this article.

The present load-balancer implements two brownout-aware algorithms on top of lighttpd: PI-Based Heuristic (PIBH) and Equality Principle-Based Heuristic (EPBH). Specifically, it looks for the X-Dimmer header in the HTTP response coming from replicas (or backend servers, in lighttpd terminology) representing the last dimmer value computed by the controller, i.e., the probability of a replica to serve a request with optional content. Based on this information, the load-balancer directs requests so as to maximize the amount of optional content served.

Our contribution does not add any new dependencies to lighttpd, hence, the usual procedure for compiling from source can be used. On Ubuntu systems, this can be achieved as follows:

# Install prerequisites
sudo apt-get install git
sudo apt-get build-dep lighttpd

# Clone source code
git clone https://github.com/cloud-control/brownout-lb-lighttpd.git

# Initialize autotools
cd brownout-lb-lighttpd
./autogen.sh

# Build
./configure
make

This implementation currently outputs a lot of statistics on standard error. We recommend executing it as follows:

src/lighttpd -Df lighttpd-brownout-test.conf -m src/.libs/ 2> exp-lb.csv >&2

The provided configuration file lighttpd-brownout-test.conf instructs lighttpd to use PIBH. For testing EPBH, edit the configuration file as suggested by the comments contained therein.

For questions or comments, please contact Cristian Klein firstname.lastname@cs.umu.se.