Debian update URL broken in repo2docker legacy builds

Does anyone know why apt-get update should have started failing recently with the following error:

Step 6/18 : RUN apt-get update
 ---> Running in 707d6fc0bb8e
Get:1 jessie/updates InRelease [44.9 kB]
Ign jessie InRelease
Ign jessie-updates InRelease
Get:2 jessie/updates/main amd64 Packages [823 kB]
Get:3 jessie Release.gpg [2,420 B]
Ign jessie-updates Release.gpg
Get:4 jessie Release [148 kB]
Ign jessie-updates Release
Get:5 jessie/main amd64 Packages [9,098 kB]
Err jessie-updates/main amd64 Packages
Err jessie-updates/main amd64 Packages
Err jessie-updates/main amd64 Packages
Err jessie-updates/main amd64 Packages
Err jessie-updates/main amd64 Packages
  404  Not Found
Fetched 10.1 MB in 2s (4,808 kB/s)
W: Failed to fetch  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
Removing intermediate container 707d6fc0bb8e
The command '/bin/sh -c apt-get update' returned a non-zero code: 100

This has started happening in the repo2docker tests (while editing the documentation). This particular bit of Dockerfile gets executed for the legacy build pack that we have to support binders that were created many years ago. They are all based on andrewosh/binder-base@sha256:eabde24f4c55174832ed8795faa40cea62fc9e2a4a9f1ee1444f8a2e4f9710ee as base image. I had a quick google to try and find the Dockerfile that produced that image but can’t find it. Does someone who is more versed in linux distros know what recently changed to make the apt-get update fail? Has the base image’s distro reached its end of life?

Jessie moved to archived state, so repo locations changed.

Use stretch-slim as base.

Can we update the URLs that are used somehow? If it has been archived we could still use it to let people keep building old repos.

The reason we support this build pack in the first place is to allow legacy repos to work. Not sure if updating it to stretch is worth it as it will break (I guess) legacy repositories. If we are going to cause breakage I’d rather just remove support for these legacy repositories and lighten our maintenance burden.

Unfortunately we don’t have any stats to tell us how many people actually rely on this :-/

Looks like is the answer to “can we update the links”.

A PR implementing this is ready for review: All our tests pass again.