CODEWITHSUNDEEP
gatling
Andreas Wederbrand
Andreas Wederbrand

Reputation: 40061

Ramp up number of calls/users until it breaks

I struggle with what seems like an easy thing to do.

I'd like to ramp up the number of concurrent calls to an api over time until it breaks.

From my understanding this is rampUsersPerSec with a low initial rate increasing to something high enough to break it with during long enough to see when it actually breaks.

This is my code

  val httpProtocol = http
    .baseUrl("http://some.url")
    .userAgentHeader("breaking test")
    .shareConnections()

  val scn = scenario("Ralph breaks it")
    .exec(
      http("root page")
      .get("/index.html")
      .check(status.is(200))
    )

  setUp(
    scn.inject(
      rampUsersPerSec(1) to 100000 during (10 minutes))
    .protocols(httpProtocol))

Two things happen

  1. I get lots of exceptions when I run it. Request Timeouts, Connection Timeouts and so on. How can I stop the test when that happens?
  2. Active Users seems much higher than expected. Did I understand 'rampUsersPerSec` wrong? What is the correct way to scale number of calls per second linear?

Upvotes: 1

Views: 1300

Answers (2)

James Warr
James Warr

Reputation: 2604

When you use rampUsersPerSec you are defining the arrival rate of users. So with 'rampUsersPerSec(1) to 100000 during (10 minutes))' gatling will inject 1 user per second at the start, and gradually increase the rate until at 10 minutes in it is injecting 100,000 users per second.

Depending on the time it takes for your call to /index.html to respond, this could very quickly out of hand as gatling isn't waiting for the users already injected to actually finish - it just keeps adding them regardless. So (roughly) in the first second gatling might inject 1 user, but then in the 2nd it might inject 166, and in the 3rd 333 users and so on. So if your scenario takes a few seconds to respond, the number of concurrent users can increase rapidly.

Unfortunately, I don't think there's any way to have the simulation detect when you've hit a defined error rate and stop. You would be better having a much slower ramp over a longer duration. Alternatively, you could use the closed form injection methods that target a given level of concurrency rather than arrival rate

Upvotes: 1

Przemek Hendel
Przemek Hendel

Reputation: 80

I'm doing similar thing to yours and I managed to solve that using below code

private val injection = incrementConcurrentUsers(1)
.times(56)
.eachLevelLasting(1700 millis)
.startingFrom(10)

Upvotes: 0

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