Crate loates

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Loates is an simple and easy load testing framework for Rust, inspired by grafana k6 and powered by tracing crate.

Although this framework covers common usecases like HTTP load testing, it is usecase agnostic. Metrics for a test is generated via use of tracing span and events inside of a user call, more about this is documented in section generating custom metrics. These spans and events are collected via a tracing subscriber.

§Concepts

Load testing is a process where an application is subjected to a specific amount of simulated load to evaluate its performance and reliability. By simulating multiple users accessing the application simultaneously, developers can identify potential bottlenecks, optimize performance, and ensure the system can handle expected traffic.

Virtual Users - Implementaion of User trait defines how to simulate this interaction with your application in ways similar to a real users. For more detail explaination look at User. Users of this framework are suppose to implement User trait for each variant of user along with their user builder function.
User Builder - A user builder function defines how to create a User instance. A User can borrow shared data from a RuntimeDataStore.
Datastores - Each execution creates a RuntimeDataStore before it begins execution, which is used to hold shared data that will be used by User.
Executors - Executors control how loates will allocate Users and perform iterations. Look at Executor docs for more details.
Scenario - Scenario is grouping of one or more executors. Scenarios are ran sequentially in order that they are defined.

§Example

More examples are available in the github repo

use std::time::Duration;

use loates::client::reqwest::Client;
use loates::prelude::*;

struct MyUser<Iter> {
    client: Client,
    post_content: Iter,
}

impl<'a, Iter> User for MyUser<Iter>
where
    Iter: Iterator<Item = &'a String> + Send,
{
    async fn call(&mut self) -> UserResult {
        // In each iteration get the next string
        let body = self.post_content.next().unwrap().to_string();
        let res = self
            .client
            .post("https://httpbin.org/anything")
            .body(body)
            .send()
            .await?;
        tokio::time::sleep(Duration::from_millis(500)).await;
        Ok(())
    }
}

async fn datastore(store: &mut RuntimeDataStore) {
    let data = vec!["a".to_string(), "b".to_string(), "c".to_string()];
    store.insert(data);
    store.insert(Client::new());
}

async fn user_builder(runtime: &RuntimeDataStore) -> impl User + '_ {
    let client: &Client = runtime.get().unwrap();
    let content: &Vec<String> = runtime.get().unwrap();

    MyUser {
        client: client.clone(),
        post_content: content.iter().cycle(),
    }
}

#[tokio::main]
async fn main() {
    let exec = Execution::builder()
        .with_user_builder(user_builder)
        .with_data(datastore)
        .with_executor(Executor::Once);

    let scenario1 = Scenario::new("scene1", exec);
    let scenarios = vec![scenario1];

    Runner::new(scenarios).enable_web(true).run().await.unwrap();
}

§Features

tui Enables tui mode, allowing for user to look at live feed of execution in terminal.
web Enables web mode which contains a simple axum server along with a inbuilt UI for looking at updates.
serde - Enable serialization with serde.
reqwest - Wrapper client type for reqwest.

§Architecture

                                      ┌───────────────────────────────────────────────┐
                                      │                    Runner                     │
                                      │  ┌──────────┐ ┌──────────┐ ┌──────────┐       │
                                      │  │  scene1  │ │  scene2  │ │  scene3  │ ....  │
     logical                          │  └──────────┘ └──────────┘ └──────────┘       │
    ┌─────────────────────────┐       │        ▼                                      │
    │Scenarios                │       │ ┌───────────────────┬───────────┐ ┌───────────┤
    │ - Scenario              │       │ │ Executor          │ datastore │ │           │
    │    - Executors          ├──────►│ │                   └─────▲─────┤ │           │
    │    - UserBuilder        │  run  │ │       ┌───────┬────────┬┘     │ │           │
    │    - DataStoreModifiers │       │ ├───────┴──┬────┴─────┬──┴──────┤ │    .....  │
    └─────────────────────────┘       │ │          │          │         │ │           │
                                      │ │  user    │  user    │  user   │ │           │
                                      │ │          │          │         │ │           │
                                      │ └──────────┴──────────┴─────────┘ └───────────┤
                                      └───────────────────────────────────────────────┘
                               traces,│
                               events │   ┌────────────┐         ┌─────────┐        ┌────┬───────┐
                                      └──►│ TRACING    ├────────►│ APP     │        │ UI ├───────┤
                                          │ SUBSCRIBER │ message │ STATE   ├──────► │    │METRICS│
                                          └────────────┘         └─────────┘        │    │       │
                                                                                    └────┴───────┘

§Tracing

Loates relies heavily on usage of tracing and tracing-subscriber to emit and collect flow of execution. Even the metrics that show up when a test runs is generated through crafted spans and events.

§Emitting metrics

To emit a custom metric from within a user task, use event macro.

The event name must be followed by a . dot and a metric type.
target for this event must to set to the constant USER_TASK
value field contains the value that you want to record.

any other fields in the event is captures as the attributes for this metric which also includes all parent span’s attributes.

event!(name: "failure.counter", target: USER_TASK, Level::INFO, value = 1u64);

There are three type of event signals that you can emit from within a user’s task.

counter - Sums all values emitted during a run and shows a counter. only accepts u64
gauge - Shows timeseries value over fixed sample range as graph. Permitted types are u64, i64, f64 or Durations as nanos (u128)
histogram - Captures p50, p90, p95, p99 values from sampled values. Permitted types are f64 or Duration as nanos (u128)

Any span(s) inside of a user task is converted to a histogram metric which would track duration of its execution as its value.

Modules§

data: Data layer for shared data
error: User error type
logical: Create test scenarios
prelude: Common imports for defining a test
runner: Running test scenarios
tracing: Trace execution of a test
user: Traits for creating virtual users

Constants§

USER_TASK: A const variable that can be used to define custom traces in your test. The tracing layer provided by this crate will ignore any events in user call that are not of this target.

Type Aliases§

UserResult

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