mirror of
https://github.com/kevinveenbirkenbach/docker-volume-backup.git
synced 2026-08-01 12:34:50 +00:00
Kevin Veen-Birkenbach
d4317827bd
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>
66 lines
2.3 KiB
Python
66 lines
2.3 KiB
Python
"""Contract of the backup CLI, in particular the snapshot flag pairing."""
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from __future__ import annotations
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import unittest
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from unittest import mock
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from baudolo.backup.cli import parse_args
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REQUIRED = ["--compose-dir", "/compose", "--backups-dir", "/backups"]
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def parse(*extra: str):
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with mock.patch("sys.argv", ["baudolo", *REQUIRED, *extra]):
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return parse_args()
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class TestSnapshotFlags(unittest.TestCase):
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def test_no_snapshot_by_default(self) -> None:
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args = parse()
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self.assertIsNone(args.snapshot)
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self.assertIsNone(args.snapshot_subject)
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def test_both_flags_together_are_accepted(self) -> None:
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args = parse("--snapshot", "btrfs", "--snapshot-subject", "/var/lib/docker")
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self.assertEqual(args.snapshot, "btrfs")
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self.assertEqual(args.snapshot_subject, "/var/lib/docker")
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def test_the_kind_alone_is_rejected(self) -> None:
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with self.assertRaises(SystemExit):
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parse("--snapshot", "btrfs")
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def test_the_subject_alone_is_rejected(self) -> None:
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with self.assertRaises(SystemExit):
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parse("--snapshot-subject", "/var/lib/docker")
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def test_an_unsupported_kind_is_rejected(self) -> None:
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with self.assertRaises(SystemExit):
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parse("--snapshot", "ext4", "--snapshot-subject", "/var/lib/docker")
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def test_zfs_is_accepted(self) -> None:
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self.assertEqual(parse("--snapshot", "zfs", "--snapshot-subject", "/d").snapshot, "zfs")
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def test_shutdown_is_rejected_because_nothing_is_stopped(self) -> None:
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with self.assertRaises(SystemExit):
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parse("--snapshot", "btrfs", "--snapshot-subject", "/d", "--shutdown")
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def test_shutdown_stays_available_without_a_snapshot(self) -> None:
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self.assertTrue(parse("--shutdown").shutdown)
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class TestRequiredFlags(unittest.TestCase):
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def test_backups_dir_is_required(self) -> None:
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with mock.patch("sys.argv", ["baudolo", "--compose-dir", "/compose"]):
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with self.assertRaises(SystemExit):
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parse_args()
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def test_compose_dir_is_required(self) -> None:
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with mock.patch("sys.argv", ["baudolo", "--backups-dir", "/backups"]):
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with self.assertRaises(SystemExit):
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parse_args()
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if __name__ == "__main__":
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unittest.main()
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