What Is Locust Load Testing

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This article will provide an explanation of the what is Locust Load Testing, Best Practices, Framework and in-depth Installation of Locust and how to use, Reviews, Shape, Websocket, advantages and disadvantages as well as examples to help you better understand each phase.

“Locust load testing is a performance testing approach that simulates user behavior to measure the scalability and performance of a system under a specific load.”

What Is Locust Load Testing

What Is Locust Load Testing Best Practices

The best practises for Locust Load Testing are explained here.

Test Environment:

  • As closely as possible, replicate the production environment in your test environment.
  • To get accurate results, use similar hardware, software settings, and network conditions.
  • Consider the database, caching layers, and external dependencies in your testing environment.
What Is Locust Load Testing Best Practices

Test Scenario Design:

  • Create test situations that are true to real user behaviour.
  • In your load testing, identify the most important user flows and give them top priority.
  • To simulate real-world usage patterns, vary the intensity of user actions like login, search, or transaction activity.

Load Distribution:

  • To accurately simulate concurrent user behaviour, distribute virtual users across multiple machines.
  • Use Locust’s distributed mode to coordinate and synchronise multiple instances of Locust running on different machines.

Test Data :

  • To perform more accurate load testing, you should use test data that is both representative and diverse.
  • Make sure your test data includes a variety of possible situations and outliers.
  • To protect sensitive information during load testing, think about using data anonymization techniques.

Ramp-up and Ramp-down:

  • To mimic realistic user growth patterns, gradually increase the load during the test.
  • Similarly, gradually reduce the load to watch how the system reacts to a lower load.
  • Using this method, any performance problems during load changes can be found.

Monitoring and Metrics:

  • During load testing, keep an eye on key performance metrics like response times, throughput, and error rates.
  • To see and analyse the data in real time, use dashboards or monitoring tools.
  • To find performance bottlenecks or anomalies, set threshold values for performance metrics.

Results Analysis:

  • Analyze and interpret the load test results in detail.
  • Find performance bottlenecks, resource constraints, or other problems that affect system performance.
  • To find areas for improvement, compare performance metrics with the system’s configuration and architecture.

Test Iteration and Collaboration:

  • To address problems and improve system performance, perform load testing in iterative cycles.
  • Share findings and work together to make improvements with developers, system administrators, and stakeholders.
  • Your load testing scripts should be continuously improved and updated to reflect changes in the application and how it is used.

By attaching to these best practises, you can enhance the effectiveness of your LLT efforts, ensure accurate simulation of user behaviour, and gain valuable insights into the performance and scalability of your system.

Locust Or Jmeter Which Is Better

  • Choose Locust if: You want to use code, need to be able to scale, and need to be able to watch in real time. It’s a great choice for software developers who want a small, adaptable tool.
  • Choose JMeter if: You need a tool that has a lot of features, an easy-to-use design, a lot of protocol support, and a strong community. It works well for complicated tasks and situations where a thorough analysis of success is important.

Locust Load Testing Example

The meaning of this will be discussed in this section along with an example.

The goal of this is to find out where the system breaks and how it acts under different levels of load. It helps developers and system administrators figure out if their app or website can handle the expected traffic or if it needs to be optimised or scaled.

this testing is made to be flexible and easy to change. Users can set up test scenarios using Python code. They can choose what tasks the locusts will do, how many users to simulate, and how fast they will make requests.

The results of the load test can be looked at to measure response times, throughput, error rates, and other performance metrics.

Here’s an example of how you can use this testing:

Scenario 1: Testing an e-commerce website’s product listing page.

  1. Test Setup:
    • Define the task: Simulate user behavior of browsing product listings.
    • Set the number of users: 100 virtual users.
    • Determine the hatch rate: 10 users per second.
  2. Test Execution:
    • Each virtual user (locust) starts by opening the website’s homepage.
    • Locusts then navigate to the product listing page, scrolling through the items.
    • They randomly click on product details to view more information.
    • After a few seconds, they return to the product listing page and repeat the process.
  3. Monitoring and Analysis:
    • During the test, performance metrics like response time and throughput are recorded.
    • The test can be run for a specific duration or until a certain condition is met.
    • After the test, the results are analyzed to identify bottlenecks or performance issues.

Scenario 2: Load testing a chat application for scalability and performance.

  1. Test Setup:
    • Define the task: Simulate user behavior of sending and receiving chat messages.
    • Set the number of users: 500 virtual users.
    • Determine the hatch rate: 50 users per second.
  2. Test Execution:
    • Each virtual user (locust) logs into the chat application.
    • Locusts initiate chat conversations by sending messages to other users.
    • They simulate receiving messages and respond accordingly.
    • The interaction continues for a specified duration or until a certain condition is met.
  3. Monitoring and Analysis:
    • Performance metrics, such as response time, message delivery rate, and concurrency, are measured and recorded.
    • The test can be customized to simulate different chat scenarios, user distributions, and message types.
    • After the test, the results are analyzed to evaluate the chat application’s performance, identify bottlenecks, and ensure scalability under heavy chat traffic.

How To Use Locust For Load Testing

Here is a step-by-step tutorial on how to use Locust for load testing:

  1. Install Locust:
    • Install Python (if not already installed).
    • Install Locust using pip: pip install locust.
  2. Create a Test Script:
    • Create a Python file for your test script (e.g., load_test.py).
    • Import the necessary modules and define your test scenarios.
  3. Define Task Behaviors:
    • Define task behaviors that your virtual users (locusts) will perform.
    • Use Locust’s API to simulate user actions like making HTTP requests, clicking buttons, etc.
  4. Set User Behavior and Load Parameters:
    • Define the number of virtual users (locusts) and their behavior.
    • Set the hatch rate to control the rate at which locusts are spawned.
  5. Run Locust:
    • Open a command prompt or terminal.
    • Navigate to the directory containing your test script.
    • Run the Locust command: locust -f load_test.py.
  6. Access the Web Interface:
    • Open a web browser and go to http://localhost:8089 (default Locust web interface).
    • Specify the number of total users and the hatch rate.
    • Click “Start Swarming” to begin the load test.
  7. Monitor and Analyze Results:
    • Monitor the live statistics and graphs in the Locust web interface during the load test.
    • After the test, review the recorded metrics and analyze the results.
  8. Customize and Iterate:
    • Modify your test script, scenarios, or load parameters as needed.
    • Repeat the load test to validate changes and optimize performance.

Also, Read What is Software Development Life Cycle

Locust Load Testing Framework

Locust Load Testing Framework is a popular open-source web application load and performance testing tool. Developers and testers can simulate thousands of concurrent users to test application performance under heavy loads.

By simulating a large number of users (locusts) interacting with the application, the Locust Load Testing Framework is intended to evaluate the performance and scalability of web applications.

Locust Load Testing Framework

Simulation: Using Python code, you can define the behaviour and actions of the simulated users in Locust user scenarios. These scenarios are portrayed as tasks that the locusts carry out, like sending HTTP requests, filling out forms, or interacting with APIs.

Distributed Testing: Locust supports distributed testing, allowing you to run the load test on multiple machines. This makes it possible to simulate real-world situations more accurately by simulating a much larger number of concurrent users.

Scalability: Locust is very scalable and can accommodate thousands of users at once on a single machine. It uses an event-driven architecture and asynchronous I/O to efficiently manage and coordinate the actions of the locusts.

Real-Time Monitoring: During a load test, Locust provides real-time monitoring and reporting of different performance metrics. It has a web-based user interface that shows the number of requests per second, response times, failures, and other useful statistics.

Flexibility: Locust is very adaptable and customizable. Based on the specific needs of your application, you can define custom behaviours and test cases. To increase its functionality, you can also add more Python libraries.

Simplicity: The framework is made to be simple to use, even for non-programmers. Locust has a simple API and a simple syntax for defining user scenarios, making it accessible to testers and developers with different levels of programming experience.

Active Community: Locust has a large and active community of users and contributors. This means that you can find a lot of documentation, tutorials, and community support to help you get started and solve any problems you might have.

Integration: Locust can work with a variety of testing tools and frameworks, including Jenkins, Docker, and cloud platforms like AWS and Google Cloud, to streamline your load testing and add it to your development pipeline.

Install Locust Load Testing

To install the Locust Load Testing Framework, follow these steps:

  1. Prerequisites: Before installing Locust, ensure that you have Python installed on your machine. Locust is compatible with Python 2.7, 3.5, 3.6, 3.7, and 3.8.
  2. Virtual Environment (optional): It’s recommended to set up a virtual environment to isolate the Locust installation from your system’s Python environment. This step ensures that the installation process doesn’t interfere with other Python packages or projects. You can use tools like virtualenv or venv to create a virtual environment.
  3. Installation: Open a terminal or command prompt and execute the following command to install Locust using pip, the Python package manager:
Locust Load Testing
  1. This command will download and install the latest version of Locust and its dependencies. If you want to install a specific version, you can specify it with the package name, like locust==1.5.3.
  2. Verify Installation: To confirm that Locust is installed correctly, run the following command:
Locust Load Testing
  1. This command will display the Locust version installed on your machine.
  2. Optional Dependencies: Locust has optional dependencies that provide additional features. For example, if you want to use the web-based user interface to monitor your load tests, you need to install the locust[web] package:
Locust Load Testing
  1. Similarly, there are other optional dependencies like locust[grpc] for gRPC support or locust[fasthttp] for faster HTTP performance. Install the required packages based on your testing needs.
  2. Verify Optional Dependencies: If you installed any optional dependencies, you can verify their installation by running:
Locust Load Testing

This command will display the available command-line options, including any additional options provided by the installed optional dependencies.

Locust Load Test Shape

In Locust, you can shape the load test by defining different patterns of user behavior. Here are some commonly used load test shapes in Locust:

  1. Constant User Load: In this shape, a constant number of locusts are spawned throughout the test, maintaining a steady load on the target application.
Locust Load Test Shape
  1. Step Load: This shape gradually increases the number of locusts over time in predefined steps. Each step represents a specific load level, allowing you to simulate a realistic increase in user traffic.
  2. Spike Load: This shape involves a sudden and significant increase in the number of locusts, simulating a spike in user traffic. It helps evaluate the application’s performance during sudden bursts of activity.
  3. Ramp Load: In a ramp load shape, the number of locusts is increased gradually over time, reaching a peak load level. It mimics a gradual increase in user traffic and helps identify performance thresholds.
  4. Soak Load: This shape involves running the load test with a constant user load over an extended period. It helps assess the application’s stability and performance under sustained high load conditions.
  5. Random Load: With this shape, the locusts randomly select tasks to execute, simulating unpredictable user behavior. It can be useful for load tests that require realistic and varied user interactions.
  6. Real User Behavior: This load test shape aims to mimic the behavior of real users by using data collected from production environments. The data is analyzed to understand typical user patterns and then replicated in the load test.
  7. Custom Load Shapes: Locust provides flexibility to define custom load test shapes based on your specific requirements. You can create complex load patterns by combining different user behaviors, adjusting task weights, and controlling the spawn rate of locusts.

Also, Read Automated Accessibility Testing Tools PDF Free Download

Locust Vs Jmeter

Click here to read Locust Vs Jmeter

Locust Vs Jmeter

Locust Load Test Websocket

WebSocket Support: The websocket package in Locust includes built-in support for testing WebSocket. To use WebSocket in Locust, you must import the necessary WebSocket libraries and classes.

Task Definition: In Locust, you create tasks that show how simulated users would act. For WebSocket load testing, you can create tasks that establish WebSocket connections, send messages, and handle responses.

The locusts carry out these tasks to make it look like multiple clients are talking to the WebSocket server.

WebSocket Client: Locust comes with a WebSocket client class that lets you create WebSocket connections within your tasks. You can use this client to send and receive messages, subscribe to specific channels, and do other WebSocket-related things.

Locust Load Test Websocket

Task Execution Flow: When you define your tasks, you need to handle the flow of WebSocket messages and responses. For example, you can use Python’s yield statement to stop a task from running until you get a response or a certain condition is met.

This enables you to simulate realistic user behaviour and interactions with the WebSocket server.

Locust Web Interface: Locust has a web-based user interface that shows statistics and test results in real time. It displays the number of connected users, requests per second, response times, and other important metrics.

You can also keep an eye on WebSocket-specific metrics, like the number of connections and messages, through the interface.

Scalability: Locust is made to be very scalable, so you can simulate a lot of WebSocket connections at once. With the help of Locust’s distributed testing feature, you can spread the load test across multiple machines and generate a lot of WebSocket traffic to stress test the WebSocket server.

Reporting and Analysis: Following the load test, Locust provides comprehensive reports and analyses of the WebSocket load test results. For additional analysis and comparison, you can export the results in different formats, like CSV or HTML. For advanced result analysis and visualisation, Locust also integrates with third-party tools and platforms.

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Locust Load Testing Advantages And Disadvantages

Advantages of Locust Load Testing:

  • Simplicity and ease of use
  • Scalability to handle thousands of simultaneous users
  • Flexibility to define custom behaviors and test cases
  • Real-time monitoring and reporting of performance metrics
  • Support for distributed testing
  • Active community with extensive resources and support
Locust Load Testing Advantages And Disadvantages

Disadvantages of Locust Load Testing:

  • Requires Python programming knowledge to define user scenarios
  • Steeper learning curve for beginners compared to GUI-based tools
  • Limited protocol support compared to some other load testing tools
  • Relatively new compared to more established load testing frameworks
  • May require additional Python libraries or integrations for specific testing requirements

Locust Load Testing Review

Locust Load Testing Framework is a powerful and flexible tool for testing web applications. Scalability, flexibility, real-time monitoring, and distributed testing capabilities are just a few of the advantages it offers.

Developers and testers can create unique user scenarios and tasks using its easy-to-use API to simulate real user behaviour.

Active community members of Locust provide extensive documentation and support. However, it requires some programming knowledge and may have a steeper learning curve than GUI-based tools.

Also, while it supports different protocols, it may only support a smaller number of them than some other load testing frameworks.

Overall, Locust is a useful tool for evaluating application performance under heavy loads and locating potential bottlenecks or problems.

Final Words

So today we learnt, What is Locust Load Testing in that we covered Best Practices, Framework and in-depth Installation of Locust and how to use, Reviews, Shape, Websocket, advantages and disadvantages as well as examples to help you better understand each phase. we have most important interview Locust load testing questions and answers.

Frequently Asked Question

Which is best for load testing?

Install Locust using pip.
Create a Locust file with your test scenarios.
Set the desired load parameters.
Start the Locust master.
Access the Locust web interface.
Configure the number of users and spawn rate.
Start the load test.
Monitor and analyze the results in the web interface.

Can I use Postman for load testing?

Yes, you can use Postman for load testing.

Can we use JMeter for load testing?


How to test API with Locust?

Install Locust using pip.
Create a Locust file and define the API tasks using the HttpUser class.
Set the desired API endpoints, headers, and payloads in the task functions.
Start the Locust master process using the command locust -f your_locust_file.py.
Access the Locust web interface and configure the number of users and spawn rate.
Start the load test and monitor the API performance and metrics in the web interface.


I'm Priyanka. I have good knowledge of Software Testing. with this blog, by sharing Software Testing knowledge I'm contributing to our Software Testing community. and trying to connect to all the software testers worldwide with this blog.

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