Spring Boot API Load Testing with Gatling

Performance matters — and in today’s world of microservices and APIs, ensuring your system can handle high traffic is non-negotiable.

Gatling is a powerful, open-source load testing tool that helps simulate thousands of users interacting with your application in real time. In this post, we’ll dive into how to perform Spring Boot API Load Testing with Gatling, using a sample REST API built with Spring Boot.

We’ll cover:

Setting up Gatling with Maven
Writing and executing load simulations
Interpreting results
Best practices for API performance testing

Spring Boot API Load Testing with Gatling

⚙️ Spring Boot Application Setup

Let’s use a simple REST API as a target for Gatling. This service returns customer data.

📁 Directory: `com.kscodes.springboot`

`CustomerController.java`

package com.kscodes.springboot.controller;

import com.kscodes.springboot.model.Customer;

import org.springframework.web.bind.annotation.*;

@RestController

@RequestMapping("/api/customers")

public class CustomerController {

@GetMapping("/{id}")

public Customer getCustomer(@PathVariable Long id) {

return new Customer(id, "Customer" + id);

}

`Customer.java`

package com.kscodes.springboot.model;

public class Customer {

private Long id;

private String name;

// Constructors, Getters, and Setters

}

🧪 Step 1: Set Up Gatling with Maven

Add the Gatling plugin to your pom.xml.

`pom.xml`

<build>

<groupId>io.gatling</groupId>

<artifactId>gatling-maven-plugin</artifactId>

<goals>

</goals>

</execution>

</executions>

</plugin>

</plugins>

</build>

Gatling simulations are written in Scala, but you don’t need deep Scala knowledge — most scripts are reusable.

🧪 Step 2: Create Simulation Script

Create your simulation under:
src/test/scala/com/kscodes/gatling/CustomerSimulation.scala

package com.kscodes.gatling

import io.gatling.core.Predef._

import io.gatling.http.Predef._

import scala.concurrent.duration._

class CustomerSimulation extends Simulation {

val httpProtocol = http

.baseUrl("http://localhost:8080") // Spring Boot URL

.acceptHeader("application/json")

val scn = scenario("Get Customer by ID")

.repeat(10) {

exec<strong>(</strong>

http("Request Customer by ID")

.get("/api/customers/1")

.check(status.is(200))

)

}

setUp(

scn.inject(

rampUsers(100).during(30.seconds) // Simulate 100 users over 30s

)

).protocols(httpProtocol)

}

🏃 Step 3: Run the Load Test

Start your Spring Boot application, then run:

./mvnw gatling:test

This will:

Launch the simulation
Generate an HTML report in:
target/gatling/<simulation-folder>/index.html

📊 Understanding the Report

Gatling generates a rich visual report showing:

Metric	Meaning
Response Time	Median, max, min durations
Requests per Second	Throughput over time
Errors	Failed vs successful requests
Percentiles	P50, P90, P99 — critical in tuning

🧠 Tips for Load Testing Spring Boot APIs

✅ Best Practices

Profile real usage
Simulate realistic user behavior — not just hammering one endpoint.
Ramp users gradually
Use rampUsers to simulate increasing load patterns.
Use realistic think time
Add pauses to reflect user delay with .pause(1.seconds)
Separate environments
Avoid testing against production unless it’s a blue/green setup.
Automate in CI
Run Gatling as part of nightly builds to detect performance regressions.

📚 Summary

In this post, you learned how to do Spring Boot API Load Testing with Gatling using:

Spring Boot REST endpoints
Gatling setup with Maven
Writing simulation scenarios
Executing load tests and reading reports

Gatling empowers you to validate the performance of your APIs under pressure and ensures your app is ready for real-world usage at scale.