Gatling — High-Performance Load Testing for Web Applications

Introduction

Gatling is an open-source load testing framework designed to measure and analyze the performance of web applications. It uses an expressive Scala-based DSL to define test scenarios as code, executes thousands of concurrent virtual users with low resource consumption, and produces interactive HTML reports. Gatling is widely used in CI pipelines for performance regression testing.

What Gatling Does

• Simulates thousands of concurrent virtual users from a single machine
• Defines load test scenarios in a readable Scala, Java, or Kotlin DSL
• Supports HTTP, WebSocket, JMS, and MQTT protocols
• Generates detailed interactive HTML reports with response time percentiles
• Integrates with Maven, Gradle, and sbt for build-system-native execution

Architecture Overview

Gatling uses a non-blocking, asynchronous architecture built on Akka actors and Netty for I/O. Each virtual user is a lightweight actor, not a thread, which allows thousands of concurrent users with minimal memory overhead. The simulation DSL compiles into an execution plan of actions (requests, pauses, loops, conditions). During execution, Gatling records all request/response metrics into a log file, which is post-processed into interactive Highcharts-based HTML reports.

Self-Hosting & Configuration

• Use the standalone bundle, or add the Gatling Maven/Gradle/sbt plugin to an existing project
• Requires Java 11 or higher to run
• Write simulations in src/test/scala (or Java/Kotlin) extending Simulation
• Configure gatling.conf for HTTP timeout, connection pooling, and report settings
• Use feeders (CSV, JSON, JDBC) to inject dynamic test data into requests

Key Features

• Actor-based architecture supports tens of thousands of virtual users per node
• Scenario DSL allows loops, conditions, pauses, and randomized user behavior
• HTML reports include response time distributions, percentiles, and error breakdowns
• Recorder tool captures browser interactions and generates simulation scripts
• Session API maintains per-user state for realistic multi-step workflows

Comparison with Similar Tools

• k6 — JavaScript-based with CLI-first workflow; Gatling uses JVM languages and produces richer HTML reports
• Locust — Python-based distributed load testing; Gatling offers higher throughput per node via non-blocking I/O
• JMeter — GUI-based XML test plans; Gatling uses code-as-test with better version control integration
• Artillery — YAML/JS load testing for Node.js; Gatling supports higher concurrency on the JVM
• Vegeta — Go CLI for constant-rate HTTP testing; Gatling provides full scenario scripting and reporting

FAQ

Q: Can I write Gatling tests in Java instead of Scala? A: Yes, Gatling 3.7+ provides a Java DSL. Tests can also be written in Kotlin.

Q: How many virtual users can Gatling handle? A: A single machine can typically simulate 10,000+ concurrent users thanks to the non-blocking actor model.

Q: Does Gatling support distributed load generation? A: The open-source version runs on a single node. Gatling Enterprise (commercial) adds multi-node distribution and real-time dashboards.

Q: Can I integrate Gatling into CI/CD? A: Yes, use the Maven or Gradle plugin to run simulations as part of the build lifecycle and fail on threshold breaches.

Sources

• https://github.com/gatling/gatling
• https://gatling.io/docs/