I saw this:
and finally this:
I initially started my search based on Duplicity, but was somewhat discouraged by the need to setup cron jobs on each server to be backed up. So I switched to looking at rsync options, which pointed me down the path of deciding whether I would pull or push from multiple servers. My most recent view however, is that I could pull from a backup server using Duplicity to get incremental backups, rather than just current state like I would get with rsync.
What is the current (2019) way of backing up (i.e. Duplicity or Duplicity-like) multiple servers? There is no LDAP or other central management at the moment. For now, the backups will be done completely managed by me and would require my intervention. Users could run their own backups by creating copies or downloading their data periodically.
My current plan is to mount all the remote server roots on my backup server and use Duplicity, like in the last link shown above, using sshfs. Duplicity would then push it directly to Backblaze B2.