mirror of
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>
34 lines
919 B
Python
34 lines
919 B
Python
"""Where a backup run puts its files, and how a finished run is stamped."""
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from __future__ import annotations
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import os
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import pathlib
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from dirval import create_stamp_file
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from .shell import execute_shell_command
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def get_machine_id() -> str:
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return execute_shell_command("sha256sum /etc/machine-id")[0][0:64]
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def stamp_directory(version_dir: str) -> None:
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"""
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Use dirval as a Python library to stamp the directory (no CLI dependency).
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"""
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create_stamp_file(version_dir)
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def create_version_directory(versions_dir: str, backup_time: str) -> str:
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version_dir = os.path.join(versions_dir, backup_time)
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pathlib.Path(version_dir).mkdir(parents=True, exist_ok=True)
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return version_dir
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def create_volume_directory(version_dir: str, volume_name: str) -> str:
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path = os.path.join(version_dir, volume_name)
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pathlib.Path(path).mkdir(parents=True, exist_ok=True)
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return path
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