doc: simplified steps for upgrading to Fedora N+2

doc/database_backup.rst

@@ -1,18 +1,50 @@
 .. _database_backup:
 
-Database backup
-===============
+Database backups
+================
 
-We periodically create a databse dump and offer users to download
-it. At the same time, it can be used as a database backup if something
-wrong happens. Please see ``/etc/cron.d/cron-backup-database-coprdb``.
+We periodically create two kinds of database dumps.
 
-To backup the database manually (this can be useful e.g. before
-upgrading to a new major version of PostgreSQL), run::
+Private/backup dump
+-------------------
+
+This "complete" dump is done for potential disaster-recovery situations.  It
+contains all the data (including private stuff like API tokens), and therefore
+we **never publish it or download it onto our machines**.  The dump is created in
+the ``/backups/`` directory on Copr Frontend, and it is periodically pulled by
+a rdiff-backup Fedora Infrastructure bot `configured by Ansible
+<https://pagure.io/fedora-infra/ansible/blob/main/f/playbooks/rdiff-backup.yml>`_.
+
+To generate the backup manually (this can be useful e.g. before upgrading to a
+new major version of PostgreSQL), run::
 
     [root@copr-fe ~][PROD]# su - postgres
     bash-5.0$ /usr/local/bin/backup-database coprdb
 
-Please be aware that the script does ``sleep`` for some
-undeterministic amount of time. You might want to kill the ``sleep``
-process to speed it up a little.
+.. warning::
+
+    Please be aware that the script does an initial ``sleep`` for some
+    undeterministic amount of time (to not backup all the Fedora Infra databases
+    at the same time).  You might want to kill the ``sleep`` process to speed it
+    up a little.  Still, be prepared that the dump, mostly because of the XZ
+    compression, takes more than 20 minutes!
+
+.. warning::
+
+    If you run this manually to have the :ref:`last-minute pre-upgrade dump
+    <how_to_upgrade_persistent_instances>`, you need to **keep the machine
+    running** till the upgrade is done — to keep the ``/backups`` directory
+    existing!
+
+Public dumps
+------------
+
+These dumps are `publicly available
+<https://copr.fedorainfracloud.org/db_dumps/>`_ for anyone's experiments.
+These are generated overnight via::
+
+    /etc/cron.d/cron-backup-database-coprdb
+
+Those dumps have all the private data filtered out (namely the contents of
+``_private`` tables), but still usable as-is for debugging purposes (e.g.
+spawning a dtesting Copr Frontend container with pre-generated database).