Comment 1 for bug 1547640

Adding dns_v4_first on to my 14.04 LTS /etc/squid-deb-proxy/squid-deb-proxy.conf solved this for me.

My personal best guess is that something happened during machine reboots in the Canonical datacenter to address the glibc updates.

My failures were to both security.ubuntu.com and archive.ubuntu.com, e.g.:

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/restricted/binary-amd64/Packages 503 Service Unavailable

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty-proposed/restricted/binary-amd64/Packages 503 Service Unavailable

(there were dozens more like this, these two were just side-by-side in scrollback.)

Thanks