Locust4k

Client library for writing Locust load test scenarios in Kotlin. This is not a full-fledged load testing framework, but facilitates communication from Worker apps (Kotlin) to Locust master (Python).

Inspired by locust4j.

Usage

Import as a Maven or Gradle dependency:

implementation("com.onepeloton.locust4k:locust4k:1.1.0")

Create one or more LocustTask implementations as demonstrated in the ExampleApp. The execute method of a LocustTask will be repeatedly invoked while the test is running. Within this method you can use your choice of networking libraries to make requests to your service under load. For each request, or series of interactions making up a scenario, invoke the success or failure callbacks to update statistics on Locust master.

Within the Locust web UI, for each "user" that you add, each Worker node that is connected to the master node will create one instance of a given LocustTask. By default, execute will be invoked as rapidly as possible. If one wishes to simulate human user behavior, Kotlin delay statements are one possible solution. However, if you are testing the saturation point of your service under load, you would typically not introduce any delays, but instead gradually increase nodes and the number of "user" units per node.

This library uses Kotlin coroutines with a minimum number of threads by default. Your LocustTask implementations must be thread safe and ideally use non-blocking coroutines. Additional control of resources and settings are exposed via the LocustWorker constructor.

Run the ExampleApp

Refer to Locust installation instructions at https://docs.locust.io/

Install Locust on macOS using Homebrew:

brew update
brew install locust

Start Locust master from the root of this project:

locust -f locust-master.py --master --master-bind-host=127.0.0.1 --master-bind-port=5557

Note locust-master.py above, which is essentially a no-op locustfile and required to start Locust.

In another terminal, run the example Worker application:

./gradlew build
./gradlew runExample -Pname=ExampleApp

Visit http://localhost:8089/ to start the load test.

Tests

We use Docker and Testcontainers to test interoperability with Locust master.

# build ExampleApp Docker image
./gradlew jibDockerBuild

# execute test suite
./gradlew test

Logging

This library includes a dependency on slf4j-api, and a SLF4J binding must be provided on the classpath in order to output logs. Log messages are succinct, with additional details set as structured logging arguments. A common practice is to output structured logs as JSON via the logstash-logback-encoder library.