it seems the CentOS 7 NetInstall.iso images of CentOS do not come with any packages…
so you will have to provide a mirror, University https://rwth-aachen.de does a magnificent job with that, even properly configured https (!)
so what you do is
- Networking is disabled per default, go to Network and put it to “on”
- go to software and type: https://ftp.halifax.rwth-aachen.de/centos/7/os/x86_64/
- find the exact directory for the version one tries to install here: https://ftp.halifax.rwth-aachen.de/centos/
- for CentOS 8 that should be: https://ftp.halifax.rwth-aachen.de/centos/8/BaseOS/x86_64/os/
- older versions that receive no updates anymore: http://vault.centos.org/
- that looks like:
Content in the BaseOS repository is intended to provide the core set of the underlying OS functionality that provides the foundation for all installations. This content is available in the RPM format and is subject to support terms similar to those in previous releases of CentOS.
Content in the AppStream repository includes additional user space applications, runtime languages, and databases in support of the varied workloads and use cases. Content in AppStream is available in one of two formats – the familiar RPM format and an extension to the RPM format called modules.