Kevin Veen-BirkenbachandClaude Opus 5
988d92534c
-a implies -D, so a generation was written with --devices --specials and rsync recreated every unix socket and fifo it found in a volume. On the swarm manager that generation lives on an nfs-ganesha export, and ganesha accepts the socket on write but cannot serve it back: the remote pull's sender then fails with readdir/readlink_stat 'Invalid argument (22)' and exits 23, deterministically, for all twelve retries - 58 minutes per run. Postfix's queue directory is the case that surfaced it, where public/ and private/ hold roughly fifty AF_UNIX sockets and nothing else. The class is wider: a discourse /shared with its in-container postgres socket, a checkmk OMD site with tmp/run/nagios.cmd, a container whose /tmp is a persisted volume. --no-D is type-based and closes all of them without anyone having to know which image binds a socket where. Nothing restorable is lost. A socket inode is meaningless after a restore; postfix's master, checkmk's omd start and discourse's supervisor recreate theirs. The whole postfix queue survives - incoming, active, deferred, hold, maildrop - so accepted-but-undelivered mail stays in the backup, which excluding the volume outright would have dropped. Device nodes go too, and the only volume that could hold them is a nested docker data root, already carrying backup: false. This is the writer side, whose source is a local docker volume. On the reader the same flag provably does nothing: rsync still stats the entry before -D decides, and getdents64 on the containing directory is outside its reach entirely. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
66 lines
2.0 KiB
Python
66 lines
2.0 KiB
Python
from __future__ import annotations
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import os
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import pathlib
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from .shell import BackupException, execute_shell_command
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def get_storage_path(volume_name: str) -> str:
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path = execute_shell_command(
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f"docker volume inspect --format '{{{{ .Mountpoint }}}}' {volume_name}"
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)[0]
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return f"{path}/"
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def get_last_backup_dir(
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versions_dir: str, volume_name: str, current_backup_dir: str
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) -> str | None:
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versions = sorted(os.listdir(versions_dir), reverse=True)
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for version in versions:
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candidate = os.path.join(versions_dir, version, volume_name, "files", "")
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if candidate != current_backup_dir and os.path.isdir(candidate):
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return candidate
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return None
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def backup_volume(
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versions_dir: str,
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volume_name: str,
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volume_dir: str,
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*,
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authoritative: bool,
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source: str,
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) -> None:
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"""Perform incremental file backup of a Docker volume.
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Args:
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authoritative: compare source and destination by content instead of by
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size and whole-second mtime. Required on a pass whose destination was
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already written from a live source, where a file can differ while
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both attributes still agree.
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source: directory to read from - the volume's mountpoint, or its path
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inside a snapshot.
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"""
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dest = os.path.join(volume_dir, "files") + "/"
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pathlib.Path(dest).mkdir(parents=True, exist_ok=True)
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last = get_last_backup_dir(versions_dir, volume_name, dest)
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link_dest = f"--link-dest='{last}'" if last else ""
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verify = "--checksum " if authoritative else ""
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cmd = (
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f"rsync -abP --no-D --delete --delete-excluded "
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f"{verify}{link_dest} {source} {dest}"
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)
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try:
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execute_shell_command(cmd)
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except BackupException as e:
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if "file has vanished" in str(e):
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print(
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"Warning: Some files vanished before transfer. Continuing.", flush=True
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)
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else:
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raise
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