Howto use apt-cacher-ng only when available?

Question

I'm using apt-cacher-ng at my local network with the following configuration on the clients:

Acquire::http { Proxy "http://acng-host:3142"; };

Some of the clients are laptops, so how do I configure them to use the cache only when it's available on this network?

Answer 1

Something like this should work:

/etc/NetworkManager/dispatcher.d

#!/bin/bash
ip=10.0.1.13
nc -w 1 $ip 3142
proxy_file="/etc/apt/apt.conf.d/02local_proxy"
if [ $? -eq 0 ]; then
    echo "Acquire::http { Proxy \"http://$ip\"; };" > $proxy_file
    echo 'Acquire::https { Proxy "false"; };' >> $proxy_file
else
    rm -f $proxy_file
fi

Fix permissions

sudo chmod +x /etc/NetworkManager/dispatcher.d/99SetAptProxy

Notes:

• The "nc" command tests that it can connect to the 3142 port on the given IP address.
• This script is run everytime the networking interfaces are changed by network manager.
• Feel free to alter the way that you detect for the proxy, this works for me, but it is a security vulnerability if you install packages on a foreign network, for example.

Answer 2

Not an exact answer, since you'll have to change your existing cache setup, but squid-deb-proxy is a good solution to providing a cache that will be used transparently if available, and is very easy to set up on both cache server and clients. See the first answer to this question for more details.