Consider the client-side application for an automated teller machine (ATM). Although each client is connected to a server, hundreds of ATMs may be open to the public. During peak times — such as 10 a.m. Monday, the start of the work week — the load may be much higher than normal. In order to test such situations, it is not practical to have a testbed of hundreds of ATMs. So, one can use an ATM simulator and a computer system with HP LoadRunner to simulate a large number of users accessing the server simultaneously. Once activities are defined, they are repeatable. After debugging a problem in the application, managers can check whether the problem persists by reproducing the same situation, with the same type of user interaction.

HP LoadRunner consists of several different tools: Virtual User Generator (VuGen), Controller, Load Generator, Analysis and the AJAX TruClient (new with V.11.0).^[4]

 Virtual User Generator

The Virtual User Generator (VuGen) is used to simulate the steps of real human users. VuGen can also run scripts for debugging.^[5] VuGen lets the user record and/or script a test to be performed against an application under test, and play back and make modifications to the script as needed, such as defining Parameterization (selecting data for keyword-driven testing).^[6]

HP LoadRunner supports more than 51 protocols including Web HTTP/HTTPS, Remote Terminal Emulator, Oracle and Web Services.^[7] A protocol acts as a communication medium between a client and a server. For example an AS400 or mainframe-based application can use a terminal emulator to talk to a server, and an on-line banking application can use HTTP/HTTPS with some Java and Web services. LoadRunner can record scripts in both single and multi-protocol modes.^[8]

During recording, VuGen records a tester's actions by routing data through a proxy.^[9] The type of proxy depends upon the protocol being used and affects the resulting script. For some protocols, various recording modes are available to further refine the resulting script. When recording web activity, HP LoadRunner allows a user to choose one of three types of recording modes: GUI based, URL based and HTML based.^[10]

Parameterization

HP LoadRunner allows users editing a script with VuGen to replace recorded values in a script with parameters. This is called parameterization.^[11]

Parameterization is often used:

When the application needs

1. Unique data (such as user name)
2. Data dependency (such as passwords)
3. Data cache
4. Date constraint

Correlation

HP LoadRunner uses Correlation to handle dynamic content. Dynamic content refers to page components that are dynamically created during the execution of a business process, and the value may differ from the value generated in a previous run. Examples of dynamic content include the ticket number in an on-line reservation system, a transaction ID in an on-line banking application and most importantly the unique session ID that is created each time a user logs in. Such dynamic values must be correlated in order to run the recorded script. The script while running will return an error if such a dynamic value has not been correlated, since the value changes each time the user logs in.

If the dynamic content is a part of a previous server response, LoadRunner can correlate that value with future instances in which it must be sent back to the server. HP LoadRunner saves the changing values into parameters, which are used during simulation.^[12]

Controller

Once a script is prepared in VuGen, it runs using the LoadRunner Controller.^[13] The Controller manages and maintains the scenarios that are run. During a scenario run, the Controller allows monitoring of network and server resources. The Controller assigns virtual users and load generators to specific scenarios.^[14]

Load Generator

Multiple machines can be set up to act as load generators in concert. To run a test of 1000 users, three or more machines can be set up with an HP LoadRunner agent installed on them. These machines are known as load generators because the actual load is generated from them. Each run is configured with a scenario that describes which scripts will run, when they will run, how many virtual users will run, and which load generators will be used for each script. The tester connects each script in the scenario to the name of a machine that is going to act as a load generator and sets the number of virtual users to be run from that load generator.This is called the working in HP load runner.^[15] HP LoadRunner can control multiple load generators and collect results, and it can control load generators located at remote networks (through a firewall) if required.^[16]

Analysis

The Analysis tool takes the result from the completed scenario and prepares graphs and reports that are used to correlate system information and identify bottlenecks and performance issues.^[17] All the graphs that contain data that may affect response time, for example, can be merged for a better understanding of the performance and to pinpoint performance problems. Once all the graphs are adjusted, an HP Load Runner report can be prepared, including related graphs, in HTML or Microsoft Word format.^[18]

HP LoadRunner in the Cloud

In May 2010, HP announced that an on-demand version of the application performance testing software would be available via Amazon Elastic Compute Cloud.^[19] HP LoadRunner in the Cloud is first being offered as beta software in the U.S. and is available with pay-as-you-go pricing. The software is intended for performance testing for businesses of any size.^[20] HP LoadRunner in the Cloud is part of a portfolio of cloud computing solutions offered by HP Software Division.^[21]