apt SRV records and debian-based docker image

apt-srv-debian-docker.md

apt/apt-get commands may use SRV record to find nearby APT service. 1

However, offical Debian/Ubuntu images cannot utilize such functonality unless /etc/services file is present.

This means APT will download packages from deb.debian.org / archive.ubuntu.com as usual. 🤣

This also means local APT (cache/proxy) servers is bypassed and the build process may be slowed down if the bandwidth is limited.

Workaround

• apt-get install -y netbase in the very beginning but this still down the package from remote.
• RUN apt-get update && apt-get install -y netbase and let docker cache this RUN command.
  Great when often rebuilt. 🛠️
• Acquire::http::Proxy but only useful in private use (proxy server usually behind firewall?) .
• Modify /etc/apt/sources.list or /etc/hosts, but cons as above.
• Modify A/CNAME record in local DNS service and point to local APT service. This is another reliability/maintenance story.

Details

When APT query SRV, it asks the service name of port 80 with getservbyport_r(), which use /etc/services, which shipped in netbase. http is not an easy answer there. Therefore, everything works as usual. 🤣

keywords for search engines

apt, apt-get, apt cache, apt proxy, srv records, dns, apt-cacher-ng, netbase, /etc/services

Only one entry of /etc/services is needed to use apt with SRV in Debian.
echo "http 80/tcp" > /etc/services will do the trick instead of install netbase.

Just google back to my own gist from https://bugs-devel.debian.org/cgi-bin/bugreport.cgi?bug=1092164
@woshikid's comment also work. But it prevent installation of netbase due to the existence of /etc/services, and the packages depend on it.