Send random request with Gatling

Question

I have a file with a Json request bodies in a file. I'd like to benchmark a web sending a constant number of requests per second, using the constantUsersPerSec(..).

However, every time a request is sent, I would like it to be taken from a list of requests (randomly, or in a loop, I don't care).

I cannot figure out how to do it with Gatling. Using the following code the request is randomly selected once and the same request is sent over and over again. Which is not what I want

My code:

class GcStressManyRequests extends Simulation{ 
  ...
  ...
    val httpProtocol: HttpProtocolBuilder = http
    .baseURL(baseUrl)
    .contentTypeHeader(contentType)  

    var requests = Source.fromResource("bodies/requests.txt").getLines().toIndexedSeq
    val random = new Random(System.currentTimeMillis())

    val scn: ScenarioBuilder = scenario("AE prod requests")
    .exec (
         http("bid_request")
         .post(endpoint)
         .body(StringBody(requests(random.nextInt(requests.length))))
         .asJSON
         .check(status.is(200))) 

         setUp(
         scn.inject(
         constantUsersPerSec(400) during (1 minutes),
         ).protocols(httpProtocol))

 }

Answer 1

I see you have your requests in a text file bodies.txt. For your task I would use a Feeder (check Step 03). With a feeder you can retrieve a random item from a list of items and use it in your calls. The steps you have to undertake to make it work:

1. Convert your text file to a csv file, a csv file just needs a header and then the values. One row for each value. Let say you name the header 'request'.

2. Create a feeder:

   val random_request = csv("bodies.csv").random
   

3. Edit scenario:

    val scn: ScenarioBuilder = scenario("AE prod requests")
      .feed(random_request) //Puts a random request in your session.
      .exec (
        http("bid_request")
        .post(endpoint)
        .body(StringBody(${request})) //Retrieve the request from current session.
        .asJSON
        .check(status.is(200))) 
   
    setUp(
      scn.inject(
      constantUsersPerSec(400) during (1 minutes),
    ).protocols(httpProtocol))
   

Answer 2

For completeness, I'd like to share Domingos Creado's answer on Gatling Google Groups that worked for me.

val scn: ScenarioBuilder = scenario("AE prod requests")
.exec(session => {
          val session2 = session.set("therequest", requests(random.nextInt(requests.length)))
          session2
        })
.exec (
     http("bid_request")
     .post(endpoint)
     .body(StringBody("${therequest}"))
     .asJSON
     .check(status.is(200)))