The kernel refuses a snapshot whose destination sits on another
filesystem. Placing it at <parent>/.baudolo-<tag> hit that on the most
sensible layout there is: a dedicated disk mounted straight onto
/var/lib/docker, where the parent directory belongs to a different
filesystem and every run failed with EXDEV.
Placing it at <subject>/.baudolo-<tag> makes source and destination the
same filesystem by construction, so the failure cannot occur on any
layout. It also aligns the two backends: the zfs path already resolves
its snapshot inside the subject, at <subject>/.zfs/snapshot/<tag>.
btrfs does not include nested subvolumes in a snapshot, so a leftover
from an interrupted run appears in the next snapshot as an empty
directory rather than recursing, and the copy only ever reads the volume
tree below it.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Four defects in the snapshot mode 3.2.0 introduced.
The resolver dropped the trailing separator get_storage_path puts on a
volume path, because os.path.abspath strips it. rsync reads "dir" as
"copy the directory" where "dir/" means "copy its contents", so every
snapshot generation landed at <volume>/files/_data/... while the live
path lands at <volume>/files/... . Restores read the live layout, and
--link-dest found nothing to match against the previous generation. The
e2e never caught it because its driver appended the separator by hand.
Snapshot teardown was fatal and masking. A busy `btrfs subvolume delete`
raised out of the finally, which skipped the generation stamp and the
compose handling on a run whose data was already complete, and replaced
whatever the body had raised. The leftover is reported instead; removing
it is a cleanup problem, not a reason to discard a good generation.
A volume created after the snapshot was taken aborted the whole run: the
volume list is enumerated inside the snapshot context, and nothing is
stopped in snapshot mode, so the host keeps creating volumes for the
duration of the copy. Such a volume is now copied live with a warning,
which is exactly what the pre-snapshot code did for it.
The snapshot pass compares by content again. 3.2.0 dropped --checksum
because a snapshot source cannot move, which is true, but the comparison
that matters is against --link-dest: a file that changed while keeping
its size and whole-second mtime was hard-linked stale out of the previous
generation, and the single snapshot pass had no authoritative pass to
repair it the way the live path does. It is still one pass against two.
--hard-restart-projects is refused alongside --snapshot, the same way
--shutdown already is: the flag exists for stacks whose database cannot
be backed up hot, which is what a snapshot removes.
Tests: the trailing separator, both teardown behaviours, the new refusal,
and app.main driving the snapshot branch - the caller that runs in
production, which no test had exercised and where the layout defect
therefore stayed invisible. The e2e driver now feeds the resolver the
string shape get_storage_path really produces.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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>
