Backing up a live volume with rsync copies a moving target: a database
written to mid-copy lands on disk in a state no engine ever committed.
Stopping the container avoids that at the cost of downtime.
A snapshot removes both. `--snapshot {btrfs,zfs}` with `--snapshot-subject`
freezes the docker root once per run, and every volume copy is then read
from that frozen tree while the containers keep serving. A restore of such
a copy is an ordinary crash recovery, which every supported engine performs
on its own at startup.
An unsupported filesystem or an unknown snapshot kind fails loudly rather
than degrading to a live copy, since a silent fallback would return exactly
the torn backup the mode exists to prevent. `--shutdown` is rejected
alongside `--snapshot` instead of being ignored: under a snapshot no
container is ever stopped, so accepting the flag would promise downtime
semantics the run does not deliver.
Copies out of a snapshot skip rsync's --checksum verification. The source
is immutable for the lifetime of the copy, so size-and-mtime cannot race,
and dropping the second full read roughly halves the I/O per volume.
backup/app.py grew past what one module could carry and is split into
layout, policy and dumps along the lines it already had internally.
Tests: unit coverage for the new snapshot, layout, policy, volume and cli
units; e2e cases drive real btrfs, zfs and ext4 filesystems on loop devices
in a privileged container, including a MariaDB that is written to across
the snapshot and must recover from the restored copy without losing a
committed row. CI installs zfs and sets E2E_REQUIRE_FILESYSTEMS so a
missing kernel module fails the build instead of silently skipping a
filesystem.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
- Handle missing or empty databases.csv gracefully with warnings and empty DataFrame
- Add unit tests for robust databases.csv loading behavior
- Adjust seed tests to assert warnings across multiple print calls
- Replace Debian docker.io with docker-ce-cli to avoid Docker API version mismatch
- Install required build tools (curl, gnupg) for Docker repo setup
https://chatgpt.com/share/697e6d9d-6458-800f-9d12-1e337509be4e
