Get Started with Load Testing

Last updated on Mar 31, 2026

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Load Testing simulates user traffic to validate your system's performance under expected and peak load conditions. Identify bottlenecks, validate scalability, and ensure your applications can handle production workloads before they face real users.

Feature Flag

Load Testing is currently behind a feature flag (CHAOS_LOAD_TESTING_ENABLED). Contact your Harness sales representative to get it enabled for your account.

Prerequisites

• Access to the Harness Resilience Testing module
• A Linux Chaos Infrastructure with load testing enabled (--load flag) configured in your project
• An environment created in your project for the infrastructure
• Target application endpoints accessible from the test infrastructure

Create your first load test

1. Navigate to Resilience Testing > Load Testing
2. Click + New Load Test

Try Sample Test

Click the + New Load Test dropdown and select Try Sample Test to instantly explore the feature with a pre-configured test: sample endpoints, realistic load settings, and example configurations included.

Step 1: Overview

Fill in the test metadata and select your infrastructure:

Field	Description
Name	A descriptive identifier for the test
Description	(Optional) What the test validates
Tags	(Optional) Labels to organize tests
Load Test Type	Select Locust (Python-based). JMeter and K6 are coming soon.
Infrastructure	Select a Linux Chaos Infrastructure (installed with the --load flag) from the dropdown

Click Next to proceed to Test Configuration.

Step 2: Test Configuration

Choose how you want to define the test workload.

Option A: Define test via UI

Use the visual editor to build HTTP scenarios without writing code. Harness generates the Locust script from your configuration at execution time.

Scenario Definition

Each request represents one HTTP call your virtual users execute on every loop. For each request:

Field	Description
Request name	Optional label to identify this request in results
HTTP Method	GET, POST, PUT, DELETE, PATCH, HEAD, or OPTIONS
URL	Full endpoint URL (e.g., https://api.example.com/users)

Each request has four tabs:

Query Parameters - Key-value pairs appended to the URL as ?key=value&key2=value2.

Headers - HTTP request headers. Common examples: Authorization: Bearer <token>, Content-Type: application/json.

Assertions - Conditions that must be true for the request to count as a success. Failed assertions are recorded as errors in results.

Assertion type	Validates
Text	Response body contains (or does not contain) a specific string
Response Time	Request completes within a specified threshold (milliseconds)

Extract from Response - Captures a dynamic value from a response (e.g., a login token) and stores it as a variable for use in later requests. Reference extracted values with {{variable_name}}.

Click + to add more requests to the scenario.

Option B: Upload Python Script

Upload a custom Locust .py script for advanced scenarios requiring custom logic, authentication flows, or complex user behavior.

Field	Description
Host URL	Base URL of the application under test. Locust prepends this to all relative paths in your script.
Script file	Drag and drop or click to browse. .py files only.

from locust import HttpUser, task, between

class WebsiteUser(HttpUser):
    wait_time = between(1, 3)

    @task
    def get_homepage(self):
        self.client.get("/")

    @task(2)
    def get_products(self):
        self.client.get("/api/products")

@task(weight) controls relative execution frequency across tasks.

Step 3: Load Configuration

Configure how virtual users are ramped up and sustained during the test:

Parameter	Description	Constraint
Number of Users	Peak concurrent virtual users	Must be a positive integer
Test Duration (seconds)	Total test runtime	Must be greater than Ramp-Up Duration
Ramp-Up Duration (seconds)	Time to reach peak users from zero	Must be less than Test Duration

Steady-state duration = Test Duration - Ramp-Up Duration.

The Load Profile graph updates in real time as you adjust values. The Load Profile Summary shows a plain-English breakdown, for example: Ramp up to 100 users in 120s · Maintain steady state for 480s · Total duration 600s (10m 0s).

Step 4: Save and Run

1. Click Save to create the load test
2. Find your test in the Load Tests list - it shows Type, Users, Duration, and Recent Executions at a glance
3. Click the Run (▶) button on any test to start an execution
4. Monitor real-time results during execution

Next Steps

• Load Test Infrastructure: Set up and manage Linux infrastructure for load tests
• Analyze Results: Understand and interpret load test execution results
• Concepts: Understand virtual users, ramp-up, assertions, and load profiles
• Chaos Testing: Combine load testing with chaos experiments for peak-load resilience validation