--- title: "Getting started with load testing through locust" url: "https://www.bekk.christmas/post/2021/20/getting-started-with-load-testing-through-locust" authors: ["Halvor Hølmebakk Mangseth"] published: "2021-12-20" updated: "2024-11-07T13:05:28Z" language: "en-US" type: "article" tags: ["Utvikling"] --- # Getting started with load testing through locust Have you heard about load testing but never really got started? Maybe you’re deploying an app to Kubernetes and have to fill out “cpu and memory requirements” and don't know how to recreate user activity? Or you’ve implemented a new feature but you’re unsure how your API handles it? Load testing is here to save you! Here's a simple quick start guide to locust to get you started. ## In short Locust is a Python load testing tool that lets you simulate concurrent users against an app and inspect request counts, errors, and graphs through a web UI. By defining tasks, wait times, start/stop hooks, and even random input in a `locustfile.py`, you can model user activity and control how aggressively endpoints are hit. - **For:** Developers who want a quick introduction to load testing with Locust - **Good to know beforehand:** Basic Python and API or web server familiarity _AI-generated_ ## What is locust? [Locust](https://locust.io/) is a nice load testing tool using python. It can swarm your app with TONS of request or fewer easily. And it has a nice web UI! ## Installing locust `pip install locust` 🤷♂️ [https://docs.locust.io/en/stable/installation.html](https://docs.locust.io/en/stable/installation.html) ## Hello World First we create a locustfile.py, which locust automatically picks up. I’ve filled mine with: _`from `_`locust `_`import `_`HttpUser, task `_`class `_`HelloWorldUser(HttpUser): @task `_`def `_`hello_world(`_`self`_`): `_`self`_`.client.get("/") `_`self`_`.client.get("/thisismy404")` We then boot up locust by running the command `locust` from the same folder as the locustfile. in the output i get a localhost address for the UI, mine showed: [http://0.0.0.0:8089](http://0.0.0.0:8089). I open this in my browser and BAM! ![locust welcome page](https://cdn.sanity.io/images/ah2n1vfr/bekk-blogg-prod/2e96a7afb0b703e0277c70c99ae5dd76aa77f4d2-1154x1462.png) I input some webserver I use for testing and see what I get when I press “start swarming”. **WARNING!** This will spam your endpoint aggressively. Maybe use a local api to test. ![load test hello world result](https://cdn.sanity.io/images/ah2n1vfr/bekk-blogg-prod/3299b9f2c63cd368b13dc566951a5e622f47b6fa-2372x776.png) Press STOP to stop it. Here we see how many successful requests we got. There are also tabs here which contains some nice graphs, an overview of different error messages and much more. Pretty neat! We can also stop it, press “new test” and for example spawn 1 user per second with up to 20 concurrent users. When that runs for a few seconds, the graph looks like this: ![load test graphs](https://cdn.sanity.io/images/ah2n1vfr/bekk-blogg-prod/da84259af4dede2408f3ed01990a06e747a8ffc5-2352x1616.png) Fancy! ## Control rate Next up, a _very_ useful feature is to control how many requests are spawned. The easiest way to control this is by setting the locust `wait_time` variable in the class. ```python from locust import HttpUser, task, between import time class HelloWorldUser(HttpUser): wait_time = between(1, 5) @task def hello_world(self): self.client.get("/") self.client.get("/thisismy404") ``` This makes each “user” wait between 1 and 5 seconds between each request. Much more controllable! ## Some different requests Locust functions start a microthread per user. The user then picks a function decorated with `@task` at random, executes that, waits the wait_time and then picks another random task. You can however weigh them. Let’s set up another task that is twice as likely to get picked. We want locust to test each of these: Example: ```python class HelloWorldUser(HttpUser): wait_time = between(1, 5) @task def hello_world(self): self.client.get("/thisismy404") @task(2) def hello_isitmeyourelookingfor(self): self.client.get("/?name=lionel") ``` We restart locust to reload the config and run it. My output looked like this: ![locust several tasks](https://cdn.sanity.io/images/ah2n1vfr/bekk-blogg-prod/e732cd2e1339c17123bc76509f59e510906db5f8-2428x668.png) Pretty cool! We technically now have everything we need to do some decent testing of endpoints. ## Start and stop functions I wanted to show another useful little thing. You can define an on_start and on_stop method, which will be executed once per user. Very useful! For example: ```python from locust import HttpUser, task, between import time class HelloWorldUser(HttpUser): wait_time = between(1, 5) @task def hello_world(self): self.client.get("/thisismy404") @task(2) def hello_isitmeyourelookingfor(self): self.client.get("/?name=lionel") def on_start(self): self.client.post("/", json={"username":"foo", "password":"bar"}) ``` ran with 10 users for a few seconds, gives this output on my webserver: ![load test with start stop](https://cdn.sanity.io/images/ah2n1vfr/bekk-blogg-prod/131ee40299b1ab4d23924cabb43fe45af4b9361d-2432x734.png) Wohoo! ## Last trick, random queries Just a last little trick if you need to get some random requests! Remember that this is just standard python, so you can for example create a task like: ```python @task def random_request(self): my_random_string = ''.join(random.choices(string.ascii_uppercase, k=10)) print(my_random_string) self.client.get(f"/{my_random_string}") ``` (remember to `import random` and `import string`). It's just an example of how we can leverage python in our locust setup, but it's quite useful. ## The End I hope this helps you get started on load testing! Sure, it’s not automated and integrated into every CI-pipeline, but it’s a lot better than just throwing stuff into prod and see what happens. Locust has tons more of awesome stuff. including a good command line interface. Check out the docs at [https://docs.locust.io/en/stable/writing-a-locustfile.html#](https://docs.locust.io/en/stable/writing-a-locustfile.html#) and the homepage at [https://locust.io/](https://locust.io/).