Benchmarking WordPress with Locust

January 15, 2021 3-minute read

locust • benchmarking • web performance • http load testing

Wordpress. Love it or hate it, it runs close to 40% of the internet. So when tasked with increasing it’s performance we need to establish a baseline and then measure our incremental changes. Queue Locust!

Install python3-venv and python dev packages
```
apt-get install python3-venv python3-dev
```

Create locust virtual environment and activate it

python3 -mvenv ~/.python_envs/locust
source ~/.python_envs/locust/bin/activate

Install locust
```
pip install locust
```

Create locustfile.py, changing https://wordpress-site.com to the site you’re testing

from locust import HttpUser, TaskSet, task, between

class WordPressTasks(TaskSet):
    @task
    def index(self):
        self.client.get("/")
    @task
    def login_page(self):
        self.client.get("/wp-login.php")

class WordPressUser(HttpUser):
    tasks = [WordPressTasks]
    host = "https://wordpress-site.com"
    wait_time = between(5, 10)

Run your test.

-u specifies the number of users

-r defines the spawn rate of the users per second

-t 2m defines the time for the tests to run
```
locust --headless -u 50 -r 10 -t2m --only-summary
```
Distribute your test. Running locust as above will limit you to a single cpu on your testing machine and you’ll likely see the following message when exceeding ~75 users:

[2021-01-16 08:16:57,407] fontani/WARNING/locust.runners: CPU usage was too high at some point during the test! See https://docs.locust.io/en/stable/running-locust-distributed.html for how to distribute the load over multiple CPU cores or machines

Locust implements a client/server model to distribute workloads across multiple CPUs or hosts. We modify our locust command above to reflect the master (sic). We define the number of expected workers and the -u, -r, and -t arguments from step 5. Increase the values as you see fit, they will be evenly distributed among the workers.
```
locust -f locustfile.py --master --headless --expect-workers=8 -u 500 -r 30 -t3m --only-summary
```
Locust will start in server mode and wait for all of the workers to join. Once all 8 are running the test will be started.
```
[2021-01-16 08:42:24,640] fontani/INFO/root: Waiting for workers to be ready, 0 of 6 connected
[2021-01-16 08:42:25,641] fontani/INFO/root: Waiting for workers to be ready, 0 of 6 connected
[2021-01-16 08:42:26,455] fontani/INFO/locust.runners: Client 'fontani_df70fddb37af2cb0aaab8a7164b20e99' reported as ready. Currently 1 clients ready to swarm.
...
[2021-01-16 09:11:18,477] fontani/INFO/locust.runners: Client 'fontani_d48661727c2a4d1b4afe54b41190e58b' reported as ready. Currently 8 clients ready to swarm.
[2021-01-16 09:11:19,134] fontani/INFO/locust.runners: Sending spawn jobs of 62 users and 3.75 spawn rate to 8 ready clients
[2021-01-16 09:11:19,137] fontani/INFO/locust.main: Run time limit set to 180 seconds
```
Fire up a screen on the host and run the following command in 8 different screens.
```
locust --headless -f locustfile.py  --worker --master-host=127.0.0.1
```

Once the testing is completed the server process will spit out a report.

Name                                                          # reqs      # fails  |     Avg     Min     Max  Median  |   req/s failures/s
--------------------------------------------------------------------------------------------------------------------------------------------
 GET /                                                           3092     0(0.00%)  |     727     411    2940     610  |   17.17    0.00
 GET /wp-login.php                                               3234     0(0.00%)  |    1145     507    3578    1000  |   17.96    0.00
--------------------------------------------------------------------------------------------------------------------------------------------
 Aggregated                                                      6326     0(0.00%)  |     941     411    3578     830  |   35.12    0.00

Response time percentiles (approximated)
 Type     Name                                                              50%    66%    75%    80%    90%    95%    98%    99%  99.9% 99.99%   100% # reqs
--------|------------------------------------------------------------|---------|------|------|------|------|------|------|------|------|------|------|------|
 GET      /                                                                 610    710    810    870   1100   1400   1900   2200   2700   2900   2900   3092
 GET      /wp-login.php                                                    1000   1200   1300   1400   1800   2000   2400   2600   3200   3600   3600   3234
--------|------------------------------------------------------------|---------|------|------|------|------|------|------|------|------|------|------|------|
 None     Aggregated                                                        830   1000   1100   1200   1500   1900   2200   2400   3200   3600   3600   6326