ab – Apache HTTP server benchmarking tool
ab is a tool for benchmarking your Apache Hypertext Transfer Protocol (HTTP) server. It is designed to give you an impression of how your current Apache installation performs. This especially shows you how many requests per second your Apache installation is capable of serving.
See following website : https://httpd.apache.org/docs/2.4/programs/ab.html
ab -n500 -c20 -H