How to Perform Load Testing on a Dockerized Web App Using Apache JMeter

Apache JMeter is a powerful open-source tool for performance testing. Here’s a detailed step by step guide to load test your web application running in Docker.

Before starting, ensure you have JMeter installed.

1.1 Install JMeter on Your Machine

• Windows & Mac:

• Download JMeter from the official site.

• Extract the downloaded .zip file.

• Navigate to the bin folder and run jmeter.bat (Windows) or jmeter (Mac/Linux).

• Linux (via Terminal):

• Docker Alternative (If you want to run JMeter inside a Docker container)

• Before running JMeter, ensure your application is up and running in Docker.
• Navigate to your project directory where your docker-compose.yml is located.
• Start the web app: docker-compose up -d
• Verify that your application is running by visiting the app URL in your browser (http://localhost:8000 or your assigned port).

A test plan defines the load test scenario. Follow these steps:

3.1 Open JMeter

• Run JMeter by executing:

A GUI will open.

3.2 Add a Thread Group (Defines Users and Load)

• Right click Test Plan → Add → Threads (Users) → Thread Group.

Configure:

• Number of Threads (Users): e.g., 100 (simulates 100 users).

• Ramp-up Period (seconds): e.g., 10 (users added over 10 sec).

• Loop Count: Forever or 5 (how many times to repeat requests).

3.3 Add an HTTP Request Sampler

• Right-click Thread Group → Add → Sampler → HTTP Request.

Configure:

• Server Name or IP: localhost (or your Docker container’s IP).

• Port: 8000 (or the port your app runs on).

• HTTP Method: GET or POST (depending on API).

• Path: /login or /api/data (endpoint you want to test).

• If it's a POST request, add Body Data or Parameters.

3.4 Add Listeners (To View Test Results)

• Right-click Thread Group → Add → Listener.

• Select View Results Tree, Summary Report or Graph Results.

   

Once the test plan is ready, execute it.

• Click the Run button in JMeter.

• Monitor the results in the View Results Tree panel.

• Analyze response times, error rates and throughput.

   

For better performance, run JMeter in command line mode:

• Save the test plan as - test_plan.jmx.

• Run JMeter using:

• -n → Non-GUI mode.  
• -t test_plan.jmx → Test plan file.
• -l results.jtl → Log file for results.

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