Simple script to configure apt to use a squid-deb-proxy server configured at the _apt-proxy._tcp SRV record for the configured search domain

Example Dockerfile

#just put this in your Dockerfile prior to doing any apt-get operations and your build will use the proxy

FROM ubuntu:14.04

RUN apt-get install -y --no-install-recommends dnsutils
ADD squid-deb-proxy-discover-setup.sh /root/
RUN /root/squid-deb-proxy-discover-setup.sh

squid-deb-proxy-discover-setup.sh

#!/bin/bash

if [ -f /etc/apt/apt.conf.d/31autoproxy ]; then
  >&2 echo "NOTICE: squid-deb-proxy-discover already installed"
  exit 0
fi

mkdir -p /usr/share/squid-deb-proxy-discover/

#we grab the search domain directly from resolv.conf because host, dig, and nslookup will
#not expand the search domain for SRV lookups.
cat > /usr/share/squid-deb-proxy-discover/squid-deb-proxy-discover << 'EOL'
#!/bin/sh
SEARCH_DOMAIN=$(grep -oP "search \K[\w\.]+" /etc/resolv.conf)
if [ ! -f /usr/bin/dig ]; then
  >&2 echo "ERROR: dig is not installed, will not set Acquire::http::ProxyAutoDetect"
  exit 1
fi
dig +short _apt_proxy._tcp.$SEARCH_DOMAIN SRV | head -n 1 | awk  '{ print "http://", $4, ":", $3};' | sed 's/ //g'
EOL

chmod +x /usr/share/squid-deb-proxy-discover/squid-deb-proxy-discover

#30autoproxy is used by squid-deb-proxy-client, which I've used for inspration here
echo 'Acquire::http::ProxyAutoDetect "/usr/share/squid-deb-proxy-discover/squid-deb-proxy-discover";' > /etc/apt/apt.conf.d/31autoproxy

I should add the reason I wanted it done like this is I wanted a single Dockerfile for an application that can move from my dev environment, to a remote dev environment, to production; where the squid-deb-proxy server is obviously different in each location.