It looks like the apt.postgresql.org repo was recently updated to have PostGIS 2.2 packages. I build a relatively popular Docker image for PostGIS, so this was great to see since it's something users have been asking to have for some time (see https://github.com/appropriate/docker-postgis).
However, it looks like in the process of updating the repo, version 2.1 of the "postgis" package was removed. This means that I can no longer build an image for PostGIS 2.1 on older Postgres versions that includes the PostGIS userland binaries.
I understand the difficulty of providing both a 2.2 package and a 2.1 package in the same repo since there is no version number in the package name (e.g. "postgis-2.1" and "postgis-2.2"), so I'm wondering how much of a loss it is to no longer have the userland binaries. I personally don't use those binaries, so I can't be sure of the impact of simply removing them from the Docker image.
