Apache Bench load testing

January 17, 2021

Apache Bench (ab) is a popular command-line tool used for benchmarking the performance of HTTP web servers. Here's a basic guide on how to use it:

Installation

Apache Bench is usually bundled with the Apache HTTP server, but it can also be installed separately. On most Unix-based systems, you can install it using your package manager. For example, on Debian, you can install it using:

apt install apache2-utils

Basic Usage

The basic syntax of Apache Bench is:

ab [options] [http[s]://]hostname[:port]/path

Key Options

• -n requests: Number of requests to perform. For benchmarking, you might start with at least 1000 requests.
• -c concurrency: Number of multiple requests to make at a time. This can be used to simulate multiple users accessing the server concurrently.
• -t timelimit: Maximum number of seconds to spend for benchmarking. This overrides the -n parameter.
• -p postfile: File containing data to POST.
• -T content-type: Content-type header to use for POST data.

Example Command

Here's an example command that sends 1000 requests to a server, with a concurrency level of 10:

ab -n 1000 -c 10 http://example.com/

Interpreting Results

After running the command, Apache Bench will provide a summary of the results, including:

• Time taken for tests
• Complete requests
• Failed requests
• Requests per second (a higher number indicates better performance)
• Time per request (both across all concurrent requests and per request)
• Transfer rate

Tips for Effective Benchmarking

1. Test in a Controlled Environment: Ensure that the testing environment is consistent for each test.
2. Monitor Server Resources: Keep an eye on server resources like CPU, memory, and disk I/O during the test.
3. Vary the Concurrency and Request Numbers: This helps you understand how your server performs under different loads.
4. Use Realistic Scenarios: If possible, use URLs and POST data that mimic actual usage patterns.

Important Considerations

• Server Impact: Running these tests can put significant load on the server, so it's best to do this on a test server or during low-traffic periods.
• Legal and Ethical Considerations: Only benchmark servers that you own or have explicit permission to test.

Apache Bench is a powerful tool for a quick assessment of HTTP server performance. For more comprehensive testing, consider other tools like JMeter or Gatling, especially for applications with more complex interactions.

Example Shell Script

Here's a small shell script to easily automate Apache Bench usage:

#!bash

N=100
C=15
AB=/usr/sbin/ab
URL=https://example.com/

$AB -n $N -c $C $URL

apache (1) test (1)