Apache Bench - Overview


Performance testing has proved itself to be crucial for the success of a business. Not only does a poor performing site face financial losses, it can also lead to legal repercussions at times.

No one wants to put up with a slow performing, unreliable site in important online interactions such as purchasing, online test taking, bill payment, etc. With the Internet being so widely available, the range of alternatives is immense. It is easier to lose clientele than gain them and performance is a key game changer.

Need for a Load Testing Tool

If we can understand what is the need for a load testing tool, it will give us the reason and motivation to use it. Some famous business sites have suffered serious downtimes when they get large number of visitors. E-commerce websites invest heavily in advertising campaigns, but not in Load Testing. Therefore, they fail to ensure optimal system performance, when that marketing brings in traffic.

Another familiar example of ignoring load testing is that of “error establishing connection” in WordPress websites. Therefore, it is a good idea to load test a website or application before its deployment in production. It is nice to quickly establish a best-case scenario for a project before running more detailed tests down the road.

What is Apache Bench?

Apache Bench (ab) is a tool from the Apache organization for benchmarking a Hypertext Transfer Protocol (HTTP) web server. Although it is designed to measure the performance of Apache web server, yet it can also be used to test any other web server that is equally good. With this tool, you can quickly know how many requests per second your web server is capable of serving.

Features of Apache Bench

Let us see the important features and limitations of Apache Bench. The features and limitations are listed below −

  • Being an open source software, it is freely available.

  • It is a simple command line computer program.

  • It is a platform-independent tool. It means that it can be invoked on Linux/Unix or on Windows server equally well.

  • It can conduct load and performance test for only web server - HTTP or HTTPS.

  • It is not extensible.

Apache Bench uses only one operating system thread irrespective of the concurrency level (specified by the -c flag). Therefore, when benchmarking high-capacity servers, a single instance of Apache Bench can itself be a bottleneck. To completely saturate the target URL, it is better to use additional instances of Apache Bench in parallel, if your server has multiple processor cores.


You need to be aware that there is no directive in the Apache Bench to increase concurrency in particular intervals while running tests. Therefore, running load tests using ab is equivalent to a denial-of-service (DOS) attack. It is recommended that you inform and take prior permission from your VPS service provider if you are going to do heavy load testing for a long period of time. They will allot you an appropriate time interval or shift your node for the load testing task.

Second, if you are testing a third person’s website continuously and for a long time just for learning Apache Bench from your VPS (which becomes the testing node), there is a remote possibility that your VPS public IP can be blocked by the third person’s website permanently. In that case, you will not be able to connect to that website with the same IP. But if you really want to connect to the website in future, the only solution will be to talk to the system administrator of the target website, or create a new instance of the server with a different IP with the help of your VPS service provider.

Having warned you, let me assure you that all tests in this tutorial are safe enough and out of what system administrators generally call "system abuse" practices.