"httpd" can be installed on any host on your Network. The only thing we should make sure that
1. All the HDP cluster Ndoes and Ambari Server host can access it without any issue.
2. On the "httpd" you can deploy ambari.repo artifacts as well as HDP/HDP-UTIL or other artifacts.
3. It is not mandatory to install httpd on amabri server host.
Firther installation instructions for offline repo can be found at: https://docs.hortonworks.com/HDPDocuments/Ambari-18.104.22.168/bk_ambari-installation/content/setting_up_a...