Welcome!

Agile Computing Authors: William Schmarzo, Liz McMillan, Gopala Krishna Behara, Sridhar Chalasani, Tirumala Khandrika

Related Topics: Microservices Expo, Java IoT, PowerBuilder, Microsoft Cloud, Agile Computing, @CloudExpo, Apache

Microservices Expo: Article

The Importance of Accurately Modeling User Interactions in Performance Testing

Take a closer look at the factors that go into creating a realistic load that will yield more accurate results

Load testing, perhaps more than any other form of testing, is one of those activities that you either choose to do well or risk a result that leaves you worse off than not doing it at all. Half-hearted attempts at load testing yield "results," but too often those results are inaccurate, leading to a false sense of security for anyone who trusts them. This, in turn, leads to the release of applications that are not adequately tested and that experience performance problems soon after entering production.

I was reminded of this not long ago, when I worked with a customer who related an experience that may sound familiar to many of you. This customer was a test engineer for a bank that had recently merged with another bank, effectively doubling their customer base. He was part of a team responsible for load testing a new web application that would serve customers from both of the original banks. Before the application was rolled out, they performed load tests and confirmed that the application could handle the expected number of users with acceptable response times. When the system went live, however, it was slow as molasses - even under user loads less than what the team had tested.

The problem, as you may have guessed, was that the team had not accurately modeled the load. The virtual users used in the testing were a homogenous group that interacted with the system in roughly the same way, from roughly the same geographic locations, at the same network speed. In reality, the customers who came from Bank A tended to perform certain transactions much more frequently than those who came from Bank B. Most of Bank B's customers lived in a different part of the country than those from Bank A. More important, customers from both banks were accessing the application at widely differing connection speeds across a range of browsers. None of these factors were modeled accurately in the load tests the team had performed. In some cases it was because the team simply had not considered them, in others it was because the load testing tool they were using provided no way to handle these differences. In either case, the result was the same; the team had given the "go live" signal to an application that was not ready, basing their decision on inaccurate load test results.

Too often, organizations take a short cut to load testing. They are focused on a single number: how many concurrent users their application will support. As a result they put little effort into script development, and they end up with an unrealistic test - one of little value. I encourage all load testers to think beyond the concurrent users metric and take a closer look at other factors that go into creating a realistic load that will yield more accurate results, including:

  • Modeling user activity
  • Modeling different connection speeds
  • Modeling different browsers and mobile devices
  • Modeling geographically distributed users

Parameterizing Scripts to Better Model User Activity
Scripts that simply record a typical user's interaction with a web application and then play it back are not going to yield accurate performance data. As an example, a script that emulates a user logging into a site, searching for a product, placing it in the cart, and checking out does little to test the performance of other user activities such as checking product reviews, accessing detailed specifications, or comparing products.

More important, if the script always logs in as the same user and orders the same product, caching effects will often skew the performance measurements, making response times shorter than they would be under a real-world load. Caching on the web server, application server, and database server all come into play, compounding any caching that is done on the client side.

To minimize caching and similar effects, scripts must be parameterized. In my example above, the script would play back different users searching for different products, and purchasing them via different methods. Ideally the script would use randomization or data customization to fill in every user editable or selectable element on each form of the web application. This script parameterization, combined with creating multiple scripts to address a variety of user interactions, produces a much more realistic user load, and it's a good idea to have a load testing tool that simplifies these tasks.

Generating a Load with a Mixture of Connection Speeds and Network Characteristics
Many testing teams use the fastest available network connections when load testing a server. The belief is that if the application performs well under those connections, it will be guaranteed to work well in production when many real-world users will have slower connections. This is a faulty assumption that leads to performance problems when the application is subjected to real-world users accessing it at a variety of network bandwidths.

Testing with only high-speed connections can mask performance problems that occur only when lower speed connections are used. Slower data speeds will require connections to the server to stay open longer, and eventually the server may reach its limit for the maximum number of open connections.

Of course, testing with only low-speed connections is equally problematic. What's needed is a reasonable mixture of virtual users accessing the server at connection speeds representative of everything from 56K modems for dial-up users to T3 lines.

With more and more users accessing the web via mobile devices, it makes sense to include 3G and 4G connection rates in the mix as well. It's also important to take into account disparities in signal strength that can cause packet loss and increased network latency. Built-in support for incorporating these factors in performance testing is increasingly important, particularly for web applications that serve a high percentage of mobile users.

Emulating Different Browsers and Native Mobile Apps
Interestingly enough (and often surprising to some), not all browsers support the same number of concurrent HTTP connections. This obviously needs to be thought of as well - if a load test models the entire user population accessing a web application with a single browser that supports four connections per server, it neglects the effects of browsers that use twice that number.

This leads to a situation similar to the one that arises with inaccurate modeling of connection speeds - with more concurrent connections, it is not unusual to see slowdowns as a server reaches its limit for simultaneous connections. To minimize these effects, load tests should apply a variety of browser profiles during playback, so that the tests identify the traffic as originating from a realistic mixture of different browsers, including mobile browsers.

Mobile devices, in fact, present a new set of challenges for load testers (see Best Practices for Load Testing Mobile Applications, Part 1 and Best Practices for Load Testing Mobile Applications, Part 2), aside from the network connection issues I've already covered. Many companies now have a separate mobile version of their site, with content tailored specifically for mobile users. Again, to perform a valid load test on such sites, a test engineer must be able to override the browser identification during playback so that the virtual user appears to be using a mobile browser.

What about native mobile applications? There is no browser involved, so you'll need a testing solution that can record, parameterize, and play back the network traffic originating from the mobile device. For some cases this can be done via a proxy, but for some apps this is not an available option. These apps may call for a tunneling approach in which the testing tool acts as a DNS server. Even if you're not facing this situation today, you may want to see if your testing tool supports this feature so you're prepared when you do need it.

Generating a Geographically Distributed Load
Unless your end-user community is accessing your application from a single location, initiating tests solely from inside your datacenter is unlikely to represent a realistic load. Such tests fail to take into account the effects of third-party servers and content delivery networks that may sit between your users and your web application.

Using the cloud to generate load as part of your testing can better model a geographically distributed user base, one that may include users from around the world, enabling test engineers to generate realistic, large-scale tests across multiple regions. Cloud testing complements internal, lab-based tests and ideally test scripts from one domain are reused in the other. With separate performance metrics for each geographic region in hand, engineers can see where performance issues are likely to arise on a region-by-region basis.

If users are accessing your web site from all over the world, load testing from the cloud helps you model that reality. When this capability is combined with tests that incorporate parameterized scripts, browser differences, support for mobile apps, and a variety of connection speeds and network effects, you can trust the accuracy of your test results.

More Stories By Steve Weisfeldt

Steve Weisfeldt is a Senior Performance Engineer at Neotys, a provider of load testing software for Web applications. Previously, he has worked as the President of Engine 1 Consulting, a services firm specializing in all facets of test automation. Prior to his involvement at Engine 1 Consulting, he was a Senior Systems Engineer at Aternity. Prior to that, Steve spent seven years at automated testing vendor Segue Software (acquired by Borland). While spending most of his time at Segue delivering professional services and training, he was also involved in pre-sales and product marketing efforts.

Being in the load and performance testing space since 1999, Steve has been involved in load and performance testing projects of all sizes, in industries that span the retail, financial services, insurance and manufacturing sectors. His expertise lies in enabling organizations to optimize their ability to develop, test and launch high-quality applications efficiently, on-time and on-budget. Steve graduated from the University of Massachusetts-Lowell with a BS in Electrical Engineering and an MS in Computer Engineering.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, examined the regulations and provided insight on how it affects technology, challenges the established rules and will usher in new levels of diligence arou...
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices t...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
The 22nd International Cloud Expo | 1st DXWorld Expo has announced that its Call for Papers is open. Cloud Expo | DXWorld Expo, to be held June 5-7, 2018, at the Javits Center in New York, NY, brings together Cloud Computing, Digital Transformation, Big Data, Internet of Things, DevOps, Machine Learning and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding busin...
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, discussed how they built...
No hype cycles or predictions of a gazillion things here. IoT is here. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
DevOps at Cloud Expo – being held June 5-7, 2018, at the Javits Center in New York, NY – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Among the proven benefits,...
@DevOpsSummit at Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, is co-located with 22nd Cloud Expo | 1st DXWorld Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
SYS-CON Events announced today that T-Mobile exhibited at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on qua...
SYS-CON Events announced today that Cedexis will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Cedexis is the leader in data-driven enterprise global traffic management. Whether optimizing traffic through datacenters, clouds, CDNs, or any combination, Cedexis solutions drive quality and cost-effectiveness. For more information, please visit https://www.cedexis.com.
SYS-CON Events announced today that Google Cloud has been named “Keynote Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Companies come to Google Cloud to transform their businesses. Google Cloud’s comprehensive portfolio – from infrastructure to apps to devices – helps enterprises innovate faster, scale smarter, stay secure, and do more with data than ever before.
SYS-CON Events announced today that Vivint to exhibit at SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California. As a leading smart home technology provider, Vivint offers home security, energy management, home automation, local cloud storage, and high-speed Internet solutions to more than one million customers throughout the United States and Canada. The end result is a smart home solution that sav...
SYS-CON Events announced today that Opsani will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Opsani is the leading provider of deployment automation systems for running and scaling traditional enterprise applications on container infrastructure.