Flow control

Beyond a straight sequence of steps, a flow can loop, branch and choose at random — covering Gatling's repeat/during/asLongAs/doIf/randomSwitch and Locust's weighted-task model in declarative YAML.

repeat — a fixed number of times

flow:
  - repeat:
      times: 3
      counter: attempt          # 0-based loop index, readable from JS (default `index`)
      steps:
        - request: { url: /poll }
        - think_time: { type: constant, duration: 1s }

while — as long as a condition holds

The condition is a JavaScript expression evaluated in the VU's runtime before each pass. max_iterations (default 10000) prevents runaway loops.

flow:
  - js: "session.vars.page = 0"
  - while:
      condition: "Number(session.vars.page) < 5"
      max_iterations: 20
      steps:
        - request: { url: "/feed?page=${page}" }
        - js: "session.vars.page = Number(session.vars.page) + 1"

if / else — branch on a condition

flow:
  - if:
      condition: "response && JSON.parse(session.vars.cart||'{}').items > 0"
      then:
        - request: { method: POST, url: /checkout }
      else:
        - request: { url: /cart/empty }

(else is optional.)

random — weighted / uniform / round-robin branches

The headline Locust paradigm (@task(weight)) and Gatling's switches. Each branch's samples are tagged with the branch name (or branch-<n>).

flow:
  - random:
      strategy: weighted          # weighted (default) | uniform | round_robin
      choices:
        - weight: 70
          name: browse
          steps:
            - request: { url: /search?q=widget }
        - weight: 25
          name: add_to_cart
          steps:
            - request: { method: POST, url: /cart, body: { json: { sku: W-1 } } }
        - weight: 5
          name: checkout
          steps:
            - request: { method: POST, url: /checkout }

Nesting

Control-flow steps nest arbitrarily — a random branch can contain a while, a repeat can wrap an if, and group still tags everything inside. This is how you model realistic user journeys: browse 1–5 pages, then with some probability add to cart, then maybe check out, retrying the payment up to 3 times. See examples/16-flow-control.yaml.