Locust Cheat Sheet

Installation

pip install locustInstall via pip
pip install locust[all]With extras
locust --versionCheck version
locust --helpShow help

Basic Script Structure

from locust import HttpUser, task, between

class WebsiteUser(HttpUser):
    wait_time = between(1, 3)  # Wait 1-3 seconds between tasks

    @task
    def index(self):
        self.client.get("/")

    @task(3)  # 3x more likely to be picked
    def about(self):
        self.client.get("/about")
          

CLI Commands

locustStart web UI (8089)
locust -f file.pySpecify file
--headlessNo web UI
-u 100Number of users
-r 10Spawn rate/sec
-t 60sRun time
-H http://hostTarget host

HTTP Methods

self.client.get()GET request
self.client.post()POST request
self.client.put()PUT request
self.client.delete()DELETE request
self.client.patch()PATCH request
self.client.head()HEAD request

Wait Time Functions

between(1, 5)Random 1-5 sec
constant(2)Fixed 2 sec
constant_pacing(5)5 sec total cycle
constant_throughput(0.5)0.5 tasks/sec

Lifecycle Events

on_start()User starts
on_stop()User stops
@events.initLocust init
@events.test_startTest begins
@events.test_stopTest ends
@events.requestEach request

POST with JSON Data

@task
def create_user(self):
    payload = {"username": "test", "email": "test@example.com"}
    headers = {"Content-Type": "application/json"}

    with self.client.post("/api/users", json=payload, headers=headers,
                          catch_response=True) as response:
        if response.status_code == 201:
            response.success()
        else:
            response.failure(f"Failed: {response.status_code}")
          

Distributed Mode

# Start master node
locust -f locustfile.py --master

# Start worker nodes (run on multiple machines)
locust -f locustfile.py --worker --master-host=192.168.1.100

# Or with expected workers
locust -f locustfile.py --master --expect-workers=4
          

Response Validation

with self.client.get("/api",
    catch_response=True) as r:
    if "success" in r.text:
        r.success()
    else:
        r.failure("Missing data")
          

TaskSet Classes

from locust import TaskSet

class UserBehavior(TaskSet):
    @task
    def browse(self):
        self.client.get("/browse")

    @task
    def stop(self):
        self.interrupt()
          

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