tsangwpx/apt-srv-debian-docker.md

## apt-srv-debian-docker.md

      
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              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
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