[ale] Backup software incompatible versions

[DJ-Pfulio]

I've been stuck on an issue for a few weeks.

For the 15 systems here, I've been using rdiff-backup v1.2.x for years,
happily. Alas, it is python2-based and newer versions are incompatible.

The current Ubuntu 20.04 includes a much newer rdiff-backup v2.0.0
which uses python3. The way that python2 and python3 pack data for
transit is different, incompatible, according to the rdiff-backup
guys.  The underlying storage format for the backup sets haven't
changed, so it is just the C/S parts.

Most of my systems are running 16.04, so they will likely move to
20.04, if that becomes possible, before next April. Some could end up on
18.04, which has a different version of rdiff-backup (python2). In
their infinite developer wisdom, someone decided that a check for
matching x.y.z rdiff-backup versions was necessary. The 'z' part
bothers me. The 'x' check makes perfect sense.

I see a number of solutions. Really addicted to the most recent
backup set effectively being an rsync mirror.  I've used
rsync+hardlinking for versions previously, but got burned due to
changes in owners and permissions not being versioned too. I'll not be
returning to the 
D D D D D D F
schedule like we used in the 1970s that some backup tools still require.

Really would rather not have to install a separate toolchain on each
system just to support backups between 3+ OS releases, but that is the
direction I'm heading.

If I wanted these sorts of complexities, I'd be running gentoo. Did
that for a few months. Never again.

For a few systems, using rsync to mirror the backup data to a location
on the backup server, then using rdiff-backup to get efficient
versioning wouldn't be too bad. In general, I only backup what is
needed to recreate the system, not ALL the bits.  My desktop backup is
just 7GB of source files. 90 days of daily versions is just 8.16GB.

Would love some other ideas.