XS Load Testing

Testing the OLPC School Server

Author: Benjamin Tran

Date: 12/15/2010

Abstract: The One Laptop Per Child (OLPC) project oversees the development, construction, and deployment of an affordable educational laptop (XO) for use in the developing countries. OLPC has been deployed in many countries and as of August 2010, there are over 1.85 million XO laptops in the field. The low-cost XOs help to revolutionize the way we educate the world's children. In the school, each child's XO laptop connects to a central server that provides various networking, content, and communication services. The server also acts as the Internet gateway if an Internet connection is available. The hardware capabilities of the server depend on factors such as cost of hardware and availability of electricity. A more powerful machine means faster access to data and the capability to handle more users simultaneously, but this usually implies higher power consumption, a luxury that is unaffordable in many parts of the world. The software that runs on the server in the classroom, called the School Server (XS), is based on the Fedora distribution of the Linux operating system and provides networking infrastructure, services, as well as education and discovery tools to the XO laptops. Among the stack of customized software included in the XS, one of the most noticeable collaborations tools included is Moodle. Moodle is a free web-based course management system. With the customized software running on limited hardware resources, how many users can reasonably connect to the server and use Moodle? What hardware combination would be ideal for use with the XS given the estimated total number of students in a school? The purpose of this project is to come up with a method to determine the approximate number of users a potential server loaded with the OLPC School Server is capable of supporting. The approach taken will be to perform functional and load testing against different hardware systems loaded with the School Server software. The project makes use of industry-standard technologies and tools such as Selenium, Apache JMeter, and nmon for Linux. Selenium ensures Moodle functions according to specifications while JMeter simulates various load against the server to test its capability. Nmon for Linux monitors server-side resources and presents graphs of CPU usage, free memory, and disk I/O activities among many others. Test results from six different machines are compared. The outcome of this project is a formal process to test and measure the capability of a potential server that is being considered for deployment.

Keywords: OLPC, One Laptop Per Child, XS School Server, XO Laptop, Moodle, Selenium, Apache JMeter, Software Testing, Functional Testing, Performance Testing, Load Testing, Stress Testing

This work is the result of taking course CSC895 Applied Research Project (Computer Science Department, San Francisco State University), with the guidance and assistance from the following advisors:

Professor Sameer Verma, College of Business, San Francisco State University

Professor Dragutin Petkovic, Department of Computer Science, San Francisco State University

Professor Barry Levine, Department of Computer Science, San Francisco State University

This work is licensed under the Creative Commons Attribution-NonCommercial 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/3.0/ or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA.

Excerpts

Methods and Approach

The purpose of this project is to come up with a method to determine the approximate number of users a potential server loaded with the OLPC School Server is capable of supporting. The approach taken will be to perform functional and load testing against different hardware systems loaded with the School Server software. Functional testing ensures that the software works the way it was intended to. Effective test cases need to be written to cover major and common use cases of the software system. Load testing involves putting variable demands onto a system and measuring its response time. This ensures the system's hardware is capable of supporting an expected number of simultaneous users at peak times. Similarly, exemplary test cases need to be written for this type of testing. The test approach needs to be defined. The review and selection of software testing tools is also of great importance. Additionally, a comprehensive but yet easy-to-use system monitoring tool must be chosen to monitor the server's resources, such as CPU and memory usage. Taking all of the required tasks into consideration, the following design objectives were finalized (with the advice of the candidate's committee members):

1. To design and write effective test cases to ensure the program's major functionality is within the scope of specifications.
2. To design and write exemplary test cases that can effectively resemble the activities and network traffic that occur when many users simultaneously access the system.
3. To select a quick and efficient approach to carry out these test cases.
4. To choose an effective functional testing framework that allows for easy creation of tests since a web application's user interface is expected to change frequently.
5. To choose an easy-to-use but yet powerful load testing tool that can simulate a heavy load with unique, dynamic data.
6. To select one or more comprehensive system monitoring tool that can graphically show the consumption of a system's resources.
7. To pick out and obtain several computer systems that can represent a broad spectrum of potential servers. The XS software will be loaded on to these systems and testing will be performed against them.
8. To write a thorough test plan containing information such as the testing environment, features to be tested, features not to be tested, test approach, hardware/software setup, etc.

All of the above design objectives that served as requirements for the project were successfully satisfied.

Full document

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