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>
88 lines
3.3 KiB
Python
88 lines
3.3 KiB
Python
"""Contract of the rsync invocation that copies a volume."""
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from __future__ import annotations
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import tempfile
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import unittest
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from pathlib import Path
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from unittest import mock
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from baudolo.backup import volume as mod
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class TestBackupVolume(unittest.TestCase):
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def copy(self, **kwargs) -> str:
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with tempfile.TemporaryDirectory() as tmp:
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defaults = {
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"versions_dir": tmp,
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"volume_name": "demo",
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"volume_dir": str(Path(tmp) / "gen" / "demo"),
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"authoritative": False,
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"source": "/var/lib/docker/volumes/demo/_data/",
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}
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defaults.update(kwargs)
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with mock.patch.object(mod, "execute_shell_command") as run:
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mod.backup_volume(
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defaults.pop("versions_dir"),
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defaults.pop("volume_name"),
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defaults.pop("volume_dir"),
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**defaults,
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)
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return run.call_args[0][0]
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def test_the_quick_check_pass_carries_no_checksum(self) -> None:
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self.assertNotIn("--checksum", self.copy(authoritative=False))
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def test_the_authoritative_pass_compares_by_content(self) -> None:
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self.assertIn("--checksum", self.copy(authoritative=True))
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def test_it_reads_from_the_given_source(self) -> None:
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command = self.copy(source="/snapshot/volumes/demo/_data/")
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self.assertIn("/snapshot/volumes/demo/_data/", command)
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def test_it_always_deletes_what_the_source_no_longer_has(self) -> None:
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self.assertIn("--delete", self.copy())
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def test_it_creates_the_destination(self) -> None:
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with tempfile.TemporaryDirectory() as tmp:
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dest = Path(tmp) / "gen" / "demo"
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with mock.patch.object(mod, "execute_shell_command"):
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mod.backup_volume(
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tmp, "demo", str(dest), authoritative=False, source="/src/"
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)
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self.assertTrue((dest / "files").is_dir())
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def test_source_is_required(self) -> None:
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with self.assertRaises(TypeError):
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mod.backup_volume("/v", "demo", "/d", authoritative=False)
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def test_authoritative_is_required(self) -> None:
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with self.assertRaises(TypeError):
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mod.backup_volume("/v", "demo", "/d", source="/src/")
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class TestLastBackupDir(unittest.TestCase):
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def test_it_ignores_the_generation_being_written(self) -> None:
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with tempfile.TemporaryDirectory() as tmp:
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current = Path(tmp) / "20260101" / "demo" / "files"
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current.mkdir(parents=True)
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found = mod.get_last_backup_dir(tmp, "demo", str(current) + "/")
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self.assertIsNone(found)
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def test_it_finds_the_previous_generation(self) -> None:
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with tempfile.TemporaryDirectory() as tmp:
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older = Path(tmp) / "20260101" / "demo" / "files"
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older.mkdir(parents=True)
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current = Path(tmp) / "20260102" / "demo" / "files"
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current.mkdir(parents=True)
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found = mod.get_last_backup_dir(tmp, "demo", str(current) + "/")
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self.assertEqual(found, str(older) + "/")
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def test_a_first_run_has_no_predecessor(self) -> None:
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with tempfile.TemporaryDirectory() as tmp:
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self.assertIsNone(mod.get_last_backup_dir(tmp, "demo", f"{tmp}/x/"))
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if __name__ == "__main__":
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unittest.main()
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