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!