mirror of
https://github.com/kevinveenbirkenbach/docker-volume-backup.git
synced 2026-08-01 12:34:50 +00:00
Kevin Veen-Birkenbach
eeaa838d02
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>
135 lines
5.2 KiB
Python
135 lines
5.2 KiB
Python
"""Contract of the filesystem snapshot used to capture volumes atomically."""
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from __future__ import annotations
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import unittest
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from baudolo.backup.shell import BackupException
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from baudolo.backup.snapshot import SnapshotError, volume_snapshot
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class Runner:
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def __init__(self, replies: dict[str, list[str]] | None = None) -> None:
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self.calls: list[str] = []
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self.replies = replies or {}
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def __call__(self, command: str) -> list[str]:
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self.calls.append(command)
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for prefix, reply in self.replies.items():
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if command.startswith(prefix):
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return reply
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return []
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class TestBtrfs(unittest.TestCase):
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def test_it_creates_a_read_only_snapshot_inside_the_subject(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(
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run.calls[0],
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"btrfs subvolume snapshot -r /var/lib/docker /var/lib/docker/.baudolo-20260731",
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)
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def test_it_removes_the_snapshot_afterwards(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(run.calls[-1], "btrfs subvolume delete /var/lib/docker/.baudolo-20260731")
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def test_it_maps_a_volume_path_into_the_snapshot(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run) as resolve:
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self.assertEqual(
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resolve("/var/lib/docker/volumes/postgres_data/_data"),
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"/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data",
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)
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def test_it_keeps_the_trailing_slash_rsync_reads_as_contents(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run) as resolve:
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self.assertEqual(
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resolve("/var/lib/docker/volumes/postgres_data/_data/"),
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"/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data/",
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)
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def test_it_removes_the_snapshot_even_when_the_body_raises(self) -> None:
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run = Runner()
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with self.assertRaises(ZeroDivisionError):
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run):
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raise ZeroDivisionError
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self.assertTrue(run.calls[-1].startswith("btrfs subvolume delete"))
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class TestZfs(unittest.TestCase):
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def _run(self) -> Runner:
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return Runner({"zfs list": ["tank/docker"]})
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def test_it_snapshots_the_dataset_mounted_at_the_subject(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertIn("zfs snapshot tank/docker@baudolo-20260731", run.calls)
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def test_it_destroys_the_snapshot_afterwards(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(run.calls[-1], "zfs destroy tank/docker@baudolo-20260731")
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def test_it_maps_a_volume_path_through_the_dot_zfs_directory(self) -> None:
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run = self._run()
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run) as resolve:
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self.assertEqual(
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resolve("/var/lib/docker/volumes/postgres_data/_data"),
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"/var/lib/docker/.zfs/snapshot/baudolo-20260731/volumes/postgres_data/_data",
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)
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def test_an_unmounted_dataset_is_an_error(self) -> None:
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run = Runner({"zfs list": [""]})
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with self.assertRaises(SnapshotError):
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with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
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pass
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class TestRejections(unittest.TestCase):
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def test_an_unknown_kind_is_rejected(self) -> None:
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run = Runner()
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with self.assertRaises(SnapshotError):
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with volume_snapshot("ext4", "/var/lib/docker", "20260731", run=run):
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pass
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self.assertEqual(run.calls, [])
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def test_a_path_outside_the_subject_is_rejected(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run) as resolve:
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with self.assertRaises(SnapshotError):
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resolve("/etc/passwd")
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def test_the_subject_itself_resolves_to_the_snapshot_root(self) -> None:
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run = Runner()
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run) as resolve:
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self.assertEqual(resolve("/var/lib/docker"), "/var/lib/docker/.baudolo-20260731")
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class Busy(Runner):
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def __call__(self, command: str) -> list[str]:
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if command.startswith("btrfs subvolume delete"):
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raise BackupException("target is busy")
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return super().__call__(command)
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class TestRemovalFailure(unittest.TestCase):
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def test_a_failed_removal_does_not_fail_a_completed_run(self) -> None:
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=Busy()):
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pass
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def test_a_failed_removal_does_not_mask_the_body(self) -> None:
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with self.assertRaises(ZeroDivisionError):
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with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=Busy()):
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raise ZeroDivisionError
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if __name__ == "__main__":
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unittest.main()
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