LoadRunner Part # 6 - Architecture

What is LoadRunner Architecture?

Broadly speaking, the architecture of LoadRunner is complex, yet easy to understand.

Suppose you are assigned to check performance of Amazon.com for 5000 users

   In a real life situation, these all these 5000 users will not be at homepage but in different section of the websites. How can we simulate different 

VUGen:

VUGen or Virtual User Generator is an IDE (Integrated Development Environment) or a rich coding editor. VUGen is used to replicate System Under Load (SUL) behaviour. VUGen provides a "recording" feature which records communication to and from client and Server in form of a coded script - also called VUser script.

So considering the above example, VUGen can record to simulate following business processes:

1. Surfing the Products Page of Amazon.com
2. Checkout
3. Payment Processing
4. Checking MyAccount Page

Controller

Once a VUser script is finalized, Controller is the main component which controls the Load simulation by managing, for example:

• How many VUsers to simulate against each business process or VUser Group
• Behaviour of VUsers (ramp up, ramp down, simultaneous or concurrent nature etc.)
• Nature of Load scenario e.g. Real Life or Goal Oriented or verifying SLA
• Which injectors to use, how many VUsers against each injector
• Collate results periodically
• IP Spoofing
• Error reporting
• Transaction reporting etc.

Taking analogy from our example controller will add following parameter to the VUGen Script

1) 3500 Users are Surfing the Products Page of Amazon.com

2) 750 Users are in Checkout

3) 500 Users are performing Payment Processing

4) 250 Users are  Checking MyAccount Page ONLY after 500 users have done Payment Processing

Even more complex scenarios are possible

1. Initiate 5 VUsers every 2 seconds till a load of 3500 VUsers (surfing Amzon product page) is achieved.
2. Iterate for 30 minutes
3. Suspend iteration for 25 VUsers
4. Re-start 20 VUSers
5. Initiate  2 users (in Checkout, Payment Processing , MyAccounts Page) every second.
6. 2500 VUsers will be generated at Machine A
7. 2500 VUsers will be generated at Machine B

Agents Machine/Load Generators/Injectors

LoadRunner Controller is responsible to simulate thousands of VUsers - these VUsers consume hardware resources for example processor and memory - hence putting a limit on the machine which is simulating them. Besides, Controller simulates these VUsers from the same machine (where Controller resides) & hence the results may not be precise. To address this concern, all VUsers are spread across various machines, called Load Generators or Load Injectors.

As a general practice, Controller resides on a different machine and load is simulated from other machines. Depending upon the protocol of VUser scripts and machine specifications, a number of Load Injectors may be required for full simulation. For example, VUsers for an HTTP script will require 2-4MB per VUser for simulation, hence 4 machines with 4 GB RAM each will be required to simulate a load of 10,000 VUsers.

Taking Analogy from our Amazon Example, the output of this component will be

Analysis:

Once Load scenarios have been executed, the role of "Analysis" component comes in.

During the execution, Controller creates a dump of results in raw form & contains information like, which version of LoadRunner created this results dump and what were configurations.

All the errors and exceptions are logged in a Microsoft access database, named, output.mdb. The "Analysis" component reads this database file to perform various types of analysis and generates graphs.

These graphs show various trends to understand the reasoning behind errors and failure under load; thus help figuring whether optimization is required in SUL, Server (e.g. JBoss, Oracle) or infrastructure.

Below is an example where bandwidth could be creating bottleneck. Let's say Web server has 1GBps capacity whereas the data traffic exceeds this capacity causing subsequent users to suffer. To determine system caters to such needs, Performance Engineer needs to analyse application behaviour with abnormal load. Below is a graph LoadRunner generates to elicit bandwidth.