Database dumps stream to the {{ offsite.bucket }} bucket
at {{ offsite.endpoint }}, with no copy kept on this server; the bucket's
own retention thins old dumps. Images and attachments go to the same
bucket's media/ folder, below.
pg_dump for the database (fast, nightly-schedulable);
tar+zstd for the images (slow, manual only). Files live in
/images/_backups/. Tag a backup to protect it
from autoprune. Set up an off-site destination above to send
database dumps off this server instead.
Nightly sends the database, then any new images and attachments. Keep last applies to this list and to any dumps still on this server.
Each file goes to the bucket's media/ folder once, named by
its fingerprint, and the bucket checks it against the fingerprint taken
at import. Only files not sent yet go in each run. With Nightly on, they
follow the database dump every night.