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Three Tips to Successfully Load Test Adobe Flex Applications
It has become increasingly important to performance test these web applications under different loads

The world has changed dramatically for organizations that use web-enabled business applications in enterprise environments. The complexities of modern applications, which include multi-tiered, globally distributed architectures, SOA and a host of other new technologies, have forced major change in the way enterprises develop, test and manage web-enabled applications. Specifically, Rich Internet Application (RIA) technologies such as Adobe Flex allow a faster, more engaging, interactive experience with browser- enabled applications and services. While an attractive option for developing expanded application capabilities these RIA technologies bring new challenges to organizations that need to deploy application features and functions in a compressed time frame and at a lower cost.

Preparing for the shift as part of this new technology trend, companies must adapt their testing approach as well. Given the way new technologies work when deployed on Onternet/intranet applications, it's important to be careful in approaching the testing of Flex applications. When rolling out next-generation applications on a mission-critical enterprise application platform, you need to be confident that your systems will perform. As load testing is one of the last crucial tasks before launching a web application, it's usually done under pressure and with tight time constraints. Before we discuss tips to make you successful when load testing Adobe Flex applications, first let's look at how Adobe Flex applications are unique.

Adobe Flex applications may be different from applications you've worked with before. For classic HTML web applications, the server does all of the processing. In addition, the rendering of HTML requires full page refreshes. Flex applications are different because content is delivered without having to reload the page. These applications download the Flash client application and run in the browser, or for Adobe AIR applications, on the desktop. The Flash is constantly being updated by the server, asynchronously. For this reason, Adobe Flex server loads reveal a very different profile.

We all know it is important to measure transaction response times when performance testing web appli­cations. But Flex technology can cause significant increases in the number of browser-to-server HTTP calls made in the background and this increase in traffic can have a profound effect on per­formance. While users might not be aware of the round-trips between the browser and a distant server, they will definitely notice performance a problem if the application is slow or doesn't work because of the increased load. Knowing the scalability limitations of your deployments is crucial.

Innovative RIA technologies like Flex present new challenges with respect to emulating a realistic load. If you're developing or deploying applications in this newer technology, successfully addressing these challenges requires thinking about load testing in new ways. Let's look at the new challenges in load testing Flex applications and three tips to improve application performance and enrich the user experience.

Tip 1: Make sure you can decode AMF and process internal identifiers
Adobe's Flex AMF (Action Messaging Format) protocol is used to exchange data between an Adobe Flash application and a database, using a Remote Procedure call. Since the data is in compressed binary format, communication is faster and more efficient than a web service. Older load testing solutions claim they can handle "Flex" technology, but have difficulty doing so in the real world. Many load testing tools rely on data being sent over HTTP and don't tap into the AMF protocol. Therefore, they don't go deep enough to understand what is being exchanged between client and server. For optimum testing, make sure your load testing tool decodes these objects so that you can parameterize the requests, extract data from the response and validate the response. Users should look for automated variable extraction and parameterization, automated comparison features to show changes from one code base to the next and automated documentation of results so test output is immediately actionable by all stakeholders.

In addition, AMF message protocol uses internal identifiers (clientId, DSId, etc.) to maintain the AMF session. Parameters in an AMF session are dynamically generated and are numerous. To avoid painful manual configuration of these parameters, make sure that your load testing tool automatically processes serialized objects and identifiers.

Tip 2: Make sure you can support customized external messages
AMF3 compact binary format helps integrate binary data exchange into all server platforms. The protocol improves the quality of all remote and messaging solutions for Flex and optimizes data exchange. AMF3 reduces the quantity of exchanged information and avoids redundant messages. In particular, AMF3 externalizable messages allow developers to customize the serialization of objects exchanged in AMF.

When selecting a load testing tool, make sure it allows you to integrate custom code into it. For optimum testing, the customized code should be loaded and run by the testing tool to correctly replay custom messages.

Tip 3: Make sure you can support polling and streaming
Many Flex applications require that some data are regularly pushed from the server to the client. Servers using AMF protocol update client data in two ways:

  • The polling method: This is when the browser queries the server at regular intervals. Technically simple in its implementation, the method's downside is that it needlessly overloads the server and is not very reactive. When these applications are recorded with a load testing tool, a high number of browsers to server requests are recorded along with other more significant requests. It's important to make sure your tool can automatically simplify your recording to get a clear maintainable script.
  • The streaming method: In this case, the client sends a single request to the server and the server responds when pertinent information is available, without closing the request. The server can send information to the client again using the same connection, without having to wait for a new request. Using this method, client data can be rapidly updated while network traffic is kept to a minimum. The testing tool must be able to keep the stream open when it plays a streaming request. This request will block the connection so the tool has to use a second connection for classic requests.

In both cases, typical HTTP response times are not useful. For regular HTTP requests, load testing tools measure the time between when the request is sent and when the response is received. It's important that your load testing tool can measure what's really interesting: the time between when the server updates the client and when the client receives the update. Not only should the tool measure this information but this function should be automated so that testing can be done frequently and earlier in the lifecycle.

As more and more companies deploy mission-critical applications on the Internet, it has become increasingly important to performance test these web applications under different loads before they go live. While Adobe Flex provides expanded capabilities to develop new powerful applications in support of organizational needs, the technology is different from other applications. As a result a new approach to load testing is required. To understand how your applications will work in the Adobe Flex production environment, and to optimize them for higher performance, you need be able to simulate not just the actions of one user, but the actions of many users. By implementing the tips in this article, companies can quickly adapt their testing methodology to handle Flex applications, get to market faster and easier than ever before, while improving productivity and saving money.

About Christophe Marton
Christophe Marton is co-founder of Neotys and co-creator of the development tool NeoLoad. Previously, he worked at Calendra where he developed his expertise in the performance and load testing space, for which he ultimately developed a unique vision for a next generation solution. While at Calendra, he developed software solutions for the identity management market which was later acquired by BMC software in 2005. During his six year tenure at Calendra, he developed the skills required to create, develop and take cutting edge software to market. Marton is a Computer Engineering graduate of ESIL Marseille Engineering School.

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