squid-deb-proxy 503 service Unavailable

Question

I have installed squid-deb-proxy in order to create a cache of packages. The command sudo apt-get update produces errors such as

Err http://mirror.dhakacom.com trusty/universe amd64 Packages
   503  Service Unavailable

and

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/main/source/Sources
   503  Service Unavailable

Here are the contents of my 02proxy file:

$ cat /etc/apt/apt.conf.d/02proxy
Acquire { HTTP { Proxy "http://localhost:8000"; }; };

However, with squid-deb-proxy removed, I face no error. What do I need to do in order to set up squid-deb-proxy?