It's not entirely dead; it's still officially under LTS. However, it no longer gets security updates from the debian security team; and the updates repos aren't available at present (should be up on archives later on).
Possible courses of action:
Wait to see if the debian:jessie images get updated to point at potential new repos one day; in the meantime, we can't build anything
Switch to using stretch
Switch to our own images based on jessie but with an updated set of apt-sources which works; but this won't get security updates because those aren't being provided any more.
https://lists.debian.org/debian-devel-announce/2019/03/msg00006.html
It's not entirely dead; it's still officially under LTS. However, it no longer gets security updates from the debian security team; and the updates repos aren't available at present (should be up on archives later on).
Possible courses of action:
I'm favoring using stretch.