Gatling Lessons learned

Introduction

This post describes a couple of best practices when using Gatling, the Scala based performance and load-testing tool.

Also one or two Scala related tips will be shown.

Lessons learned

1. You can't set a header-field in the header like this in a scenario:
   
   .header("request-tracing-id", UUID.randomUUID().toString())
   
   This is because the scenario is only created once, and unless you use session variables it, it is all static (a function).
   
   To solve this one can use a feeder, like this:
   
   val feeder = Iterator.continually(Map("traceHeader" -> UUID.randomUUID().toString))
   
   And then replace the UUID.randomUUID().toString() line with:
   
   .header("request-trace-id", "${traceHeader}")
   
   
2. A Scala 2.11 example of a ternary (maybe not the best solution Scala-wise but readable :)
   
   .value(availableBalanceDecimal, if (dto.availableBalanceDecimal.isEmpty) null else dto.availableBalanceDecimal.get)
   
   
3. Connecting correctly to a service with a Gatling test in one environment (Nginx, ingress, Kubernetes) for some reason did not work. But it was able to connect to the service under test correctly in another environment. Apparently it had something to do with a proxy in between because had to add .proxy() and it worked:
   
   val httpConf = http
   .baseURL("http://172.20.33.101:30666") // Here is the root for all relative URLs
   .header(HttpHeaderNames.ContentType, HttpHeaderValues.ApplicationJson)
   .header(HttpHeaderNames.Accept, HttpHeaderValues.ApplicationJson)
   .proxy(Proxy("performance.project.com", 30666))   // note it is the *same* machine as the baseURL,but specified by name... 
   
   
4. A .check() with in it a .saveAs() will *not* happen when the earlier expression evaluates to false, or the conversion fails.
   Kindof makes sense when evaluates to false, but you might miss this one; or maybe you don't even want this .is() because all it means now only isFinished will be set to FINISHED and else it won't be set in the below example.
   
   someText is always found in the session, but the other one, isFinished, is not.
   
   .check(jsonPath("$[0].status").saveAs("someText"))
   .check(jsonPath("$[0].status").is("FINISHED").saveAs("isFinished"))
   ...
   .exec(session => {
      val isFinished = session.get("isFinished").asOption[String]
      logger.debug("Generated isFinished = {}", isFinished.getOrElse("Could not find expected isFinished..."))
      session
   })
   .doIf(session =>
      (!session.get("someText").as[String].equals("FINISHED") ||
      session.get("isFinished").as[Boolean].equals(false)
   ))(
   ...
   
   When running at DEBUG level the above logs:
      Session(Map(someText -> TIMED_OUT, ...)  /// So .saveAs() ocurred
      13:45:56.983 [DEBUG] SomeSimulation - Generated isFinished = Could not find expected isFinished...  
   
   So the second.saveAs() did not occur for isFinished at all, since it is not set to true nor false; it is not set at all!
   
   

Best of this Week Summary 17 May - 23 May 2010

• Codelab ("tutorial") from Google that "shows how web application vulnerabilities can be exploited and how to defend against these attacks. The best way to learn things is by doing, so you'll get a chance to do some real penetration testing, actually exploiting a real application. The codelab is built around Jarlsberg, a small, cheesy web application that allows its users to publish snippets of text and store assorted files. "Unfortunately," Jarlsberg has multiple security bugs ranging from cross-site scripting and cross-site request forgery, to information disclosure, denial of service, and remote code execution. The goal of this codelab is to guide you through discovering some of these bugs and learning ways to fix them both in Jarlsberg and in general."
  


• A new IBM Redbook on WebSphere Messaging and High Availability has just been released.
  


• A cool Android with Hudson continuous integration. Led on mobile phone changes color depending on the build status. Remember the Lava Lamps version?
  


• Java dynamic proxies explained. They are for example used in Hibernate for lazy loading entities and in Spring for AOP. Also explains what CGLib proxies are for.
  

Best of this Week Summary 13 July - 19 July 2009

• Pretty basic SOAP monitor (proxy) that allows you to edit SOAP messages before sending them on. Does not support a proxy (yet).
  


• IBM recently released Milepost GCC (website has styling from 1998 ;), a "compiler which analyses the software and determines which code optimizations will be most effective during compilation using machine learning techniques. Experiments carried out with the compiler achieved an average 18% performance improvement. The compiler is expected to significantly reduce time-to-market of new software, because lengthy manual optimization can now be carried out by the compiler." Related to that is also the Collective Tuning wiki, dedicated to developing self-tuning computing systems.
  


• ZeroTurnaround "has released the results of their "Java EE Containers - Heaven or Hell" survey. Using responses from 700 respondents, they cover topics such as: containers most often used on large projects, fastest container, redeploy times and annual costs of redeployment in a series of charts and calculations. Both the charts and raw data are made available for your own analysis."
  


• Looking for petabyte and beyond scale storage? The opensource project Ceph might be an option: it is a distributed network file system designed to provide excellent performance, reliability, and scalability.
  


• Several basic and advanced JPA implementation patterns can be found here.