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https://github.com/kevinveenbirkenbach/docker-volume-backup.git
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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>
42 lines
1.2 KiB
Python
42 lines
1.2 KiB
Python
"""Copy a live database's volume out of a snapshot, using the real backup path.
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Runs inside the privileged container built by test_e2e_snapshot_db.py, where a
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database is mid-write on a btrfs subvolume. Exercises volume_snapshot and
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backup_volume exactly as a backup run would.
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"""
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from __future__ import annotations
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import subprocess
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import sys
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sys.path.insert(0, "/src")
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from baudolo.backup.snapshot import SnapshotError, volume_snapshot # noqa: E402
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from baudolo.backup.volume import backup_volume # noqa: E402
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SUBJECT = "/subject/docker"
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VOLUME = "mariadb_data"
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DATADIR = f"{SUBJECT}/volumes/{VOLUME}/_data"
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VERSIONS = "/backups"
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GENERATION = f"{VERSIONS}/20260731"
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def shell(command: str) -> list[str]:
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proc = subprocess.run(command, shell=True, capture_output=True, text=True)
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if proc.returncode != 0:
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raise SnapshotError(f"{command} exited {proc.returncode}: {proc.stderr.strip()}")
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return proc.stdout.splitlines()
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with volume_snapshot("btrfs", SUBJECT, "dbtest", run=shell) as resolve:
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backup_volume(
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VERSIONS,
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VOLUME,
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f"{GENERATION}/{VOLUME}",
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authoritative=False,
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source=resolve(DATADIR) + "/",
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)
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print("SNAPSHOT COPY DONE", flush=True)
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