setting up apt-cacher-ng clients

client setup

nmap -p 3142 x.x.x.x
vi /etc/apt/apt.conf.d/01proxy

Acquire::http { Proxy "http://x.x.x.x:3142"; };

or against a specific repository

Acquire::http::Proxy::external.repo.host "http://your.proxy.host/";

apply

apt update

resources

client setup

https://serverfault.com/questions/482318/apt-get-proxy-for-specific-repos