How to install Apache Benchmark on CentOS?
You can discover which package contains the program you want using yum provides:
yum provides /usr/bin/ab
Then you will see that ab is in the httpd-tools package.
And now you can install it:
yum install httpd-tools
Beginning with RHEL/CentOS 7, you can also supply a filename contained within a package, and yum will automatically locate and install the corresponding package.
yum install /usr/bin/ab # RHEL 7
dnf install /usr/bin/ab # RHEL 8