Did you try apt-get update in debian 8? It was easy in the old days, but not today.
Why? Debian 8 reached end of life. By default, apt will get the update from http://httpredir.debian.org/debian. However, this site no longer contains the update/packages for debian 8.
If you search ‘apt-get update debian 8’ , you’ll find a lot of information, but most of them no longer work. (e.g. use http://archive.debian.org but the signature was expired).
Warning!!! The following will make your system insecure
In order to make apt works, change the /etc/apt/sources.list file to
deb [trusted=yes] http://archive.debian.org/debian jessie main contrib non-free
deb [trusted=yes] http://archive.debian.org/debian jessie-backports main contrib non-free
deb [trusted=yes] http://archive.debian.org/debian-security jessie/updates main contrib non-free
deb-src [trusted=yes] http://archive.debian.org/debian/ jessie main contrib non-free"
You should make your own modifications to fit your requirements like removing deb-src line, removing non-free, removing backports, etc. Please bear in mind the keyring/signature expiration message is still shown when you run apt/apt-get.
Since the above change will always trust the non-https site, a better solution (still insecure) is to use “apt-transport-https” and change http to https.
For docker, simple add the following to the Dockerfile
RUN echo "deb [trusted=yes] http://archive.debian.org/debian jessie contrib main non-free" > /etc/apt/sources.list \
&& echo "deb [trusted=yes] http://archive.debian.org/debian jessie-backports main contrib non-free" >> /etc/apt/sources.list \
&& echo "deb [trusted=yes] http://archive.debian.org/debian-security jessie/updates main contrib non-free" >> /etc/apt/sources.list \
&& echo "deb-src [trusted=yes] http://archive.debian.org/debian/ jessie main contrib non-free" >> /etc/apt/sources.list