mailinabox/management/backup.py

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2014-06-03 20:21:17 +00:00
#!/usr/bin/python3
# This script performs a backup of all user data:
# 1) System services are stopped while a copy of user data is made.
# 2) An incremental encrypted backup is made using duplicity into the
# directory STORAGE_ROOT/backup/encrypted. The password used for
# encryption is stored in backup/secret_key.txt.
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# 3) The stopped services are restarted.
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# 5) STORAGE_ROOT/backup/after-backup is executd if it exists.
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import os, os.path, shutil, glob, re, datetime
import dateutil.parser, dateutil.relativedelta, dateutil.tz
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from utils import exclusive_process, load_environment, shell
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# Destroy backups when the most recent increment in the chain
# that depends on it is this many days old.
keep_backups_for_days = 3
def backup_status(env):
# What is the current status of backups?
# Loop through all of the files in STORAGE_ROOT/backup/encrypted to
# get a list of all of the backups taken and sum up file sizes to
# see how large the storage is.
now = datetime.datetime.now(dateutil.tz.tzlocal())
def reldate(date, ref, clip):
if ref < date: return clip
rd = dateutil.relativedelta.relativedelta(ref, date)
if rd.months > 1: return "%d months, %d days" % (rd.months, rd.days)
if rd.months == 1: return "%d month, %d days" % (rd.months, rd.days)
if rd.days >= 7: return "%d days" % rd.days
if rd.days > 1: return "%d days, %d hours" % (rd.days, rd.hours)
if rd.days == 1: return "%d day, %d hours" % (rd.days, rd.hours)
return "%d hours, %d minutes" % (rd.hours, rd.minutes)
backups = { }
backup_root = os.path.join(env["STORAGE_ROOT"], 'backup')
backup_dir = os.path.join(backup_root, 'encrypted')
os.makedirs(backup_dir, exist_ok=True) # os.listdir fails if directory does not exist
for fn in os.listdir(backup_dir):
m = re.match(r"duplicity-(full|full-signatures|(inc|new-signatures)\.(?P<incbase>\d+T\d+Z)\.to)\.(?P<date>\d+T\d+Z)\.", fn)
if not m: raise ValueError(fn)
key = m.group("date")
if key not in backups:
date = dateutil.parser.parse(m.group("date"))
backups[key] = {
"date": m.group("date"),
"date_str": date.strftime("%x %X"),
"date_delta": reldate(date, now, "the future?"),
"full": m.group("incbase") is None,
"previous": m.group("incbase"),
"size": 0,
}
backups[key]["size"] += os.path.getsize(os.path.join(backup_dir, fn))
# Ensure the rows are sorted reverse chronologically.
# This is relied on by should_force_full() and the next step.
backups = sorted(backups.values(), key = lambda b : b["date"], reverse=True)
# Get the average size of incremental backups and the size of the
# most recent full backup.
incremental_count = 0
incremental_size = 0
first_full_size = None
for bak in backups:
if bak["full"]:
first_full_size = bak["size"]
break
incremental_count += 1
incremental_size += bak["size"]
# Predict how many more increments until the next full backup,
# and add to that the time we hold onto backups, to predict
# how long the most recent full backup+increments will be held
# onto. Round up since the backup occurs on the night following
# when the threshold is met.
deleted_in = None
if incremental_count > 0 and first_full_size is not None:
deleted_in = "approx. %d days" % round(keep_backups_for_days + (.5 * first_full_size - incremental_size) / (incremental_size/incremental_count) + .5)
# When will a backup be deleted?
saw_full = False
days_ago = now - datetime.timedelta(days=keep_backups_for_days)
for bak in backups:
if deleted_in:
# Subsequent backups are deleted when the most recent increment
# in the chain would be deleted.
bak["deleted_in"] = deleted_in
if bak["full"]:
# Reset when we get to a full backup. A new chain start next.
saw_full = True
deleted_in = None
elif saw_full and not deleted_in:
# Mark deleted_in only on the first increment after a full backup.
deleted_in = reldate(days_ago, dateutil.parser.parse(bak["date"]), "on next daily backup")
bak["deleted_in"] = deleted_in
return {
"directory": backup_dir,
"encpwfile": os.path.join(backup_root, 'secret_key.txt'),
"tz": now.tzname(),
"backups": backups,
}
def should_force_full(env):
# Force a full backup when the total size of the increments
# since the last full backup is greater than half the size
# of that full backup.
inc_size = 0
for bak in backup_status(env)["backups"]:
if not bak["full"]:
# Scan through the incremental backups cumulating
# size...
inc_size += bak["size"]
else:
# ...until we reach the most recent full backup.
# Return if we should to a full backup.
return inc_size > .5*bak["size"]
else:
# If we got here there are no (full) backups, so make one.
# (I love for/else blocks. Here it's just to show off.)
return True
def perform_backup(full_backup):
env = load_environment()
exclusive_process("backup")
backup_root = os.path.join(env["STORAGE_ROOT"], 'backup')
backup_cache_dir = os.path.join(backup_root, 'cache')
backup_dir = os.path.join(backup_root, 'encrypted')
# In an older version of this script, duplicity was called
# such that it did not encrypt the backups it created (in
# backup/duplicity), and instead openssl was called separately
# after each backup run, creating AES256 encrypted copies of
# each file created by duplicity in backup/encrypted.
#
# We detect the transition by the presence of backup/duplicity
# and handle it by 'dupliception': we move all the old *un*encrypted
# duplicity files up out of the backup/duplicity directory (as
# backup/ is excluded from duplicity runs) in order that it is
# included in the next run, and we delete backup/encrypted (which
# duplicity will output files directly to, post-transition).
old_backup_dir = os.path.join(backup_root, 'duplicity')
migrated_unencrypted_backup_dir = os.path.join(env["STORAGE_ROOT"], "migrated_unencrypted_backup")
if os.path.isdir(old_backup_dir):
# Move the old unencrpyted files to a new location outside of
# the backup root so they get included in the next (new) backup.
# Then we'll delete them. Also so that they do not get in the
# way of duplicity doing a full backup on the first run after
# we take care of this.
shutil.move(old_backup_dir, migrated_unencrypted_backup_dir)
# The backup_dir (backup/encrypted) now has a new purpose.
# Clear it out.
shutil.rmtree(backup_dir)
# On the first run, always do a full backup. Incremental
# will fail. Otherwise do a full backup when the size of
# the increments since the most recent full backup are
# large.
full_backup = full_backup or should_force_full(env)
# Stop services.
shell('check_call', ["/usr/sbin/service", "dovecot", "stop"])
shell('check_call', ["/usr/sbin/service", "postfix", "stop"])
# Get the encryption passphrase. secret_key.txt is 2048 random
# bits base64-encoded and with line breaks every 65 characters.
# gpg will only take the first line of text, so sanity check that
# that line is long enough to be a reasonable passphrase. It
# only needs to be 43 base64-characters to match AES256's key
# length of 32 bytes.
with open(os.path.join(backup_root, 'secret_key.txt')) as f:
passphrase = f.readline().strip()
if len(passphrase) < 43: raise Exception("secret_key.txt's first line is too short!")
env_with_passphrase = { "PASSPHRASE" : passphrase }
# Update the backup mirror directory which mirrors the current
# STORAGE_ROOT (but excluding the backups themselves!).
try:
shell('check_call', [
"/usr/bin/duplicity",
"full" if full_backup else "incr",
"--archive-dir", backup_cache_dir,
"--exclude", backup_root,
"--volsize", "250",
"--gpg-options", "--cipher-algo=AES256",
env["STORAGE_ROOT"],
"file://" + backup_dir
],
env_with_passphrase)
finally:
# Start services again.
shell('check_call', ["/usr/sbin/service", "dovecot", "start"])
shell('check_call', ["/usr/sbin/service", "postfix", "start"])
# Once the migrated backup is included in a new backup, it can be deleted.
if os.path.isdir(migrated_unencrypted_backup_dir):
shutil.rmtree(migrated_unencrypted_backup_dir)
# Remove old backups. This deletes all backup data no longer needed
# from more than 3 days ago.
shell('check_call', [
"/usr/bin/duplicity",
"remove-older-than",
"%dD" % keep_backups_for_days,
"--archive-dir", backup_cache_dir,
"--force",
"file://" + backup_dir
],
env_with_passphrase)
# From duplicity's manual:
# "This should only be necessary after a duplicity session fails or is
# aborted prematurely."
# That may be unlikely here but we may as well ensure we tidy up if
# that does happen - it might just have been a poorly timed reboot.
shell('check_call', [
"/usr/bin/duplicity",
"cleanup",
"--archive-dir", backup_cache_dir,
"--force",
"file://" + backup_dir
],
env_with_passphrase)
# Change ownership of backups to the user-data user, so that the after-bcakup
# script can access them.
shell('check_call', ["/bin/chown", "-R", env["STORAGE_USER"], backup_dir])
# Execute a post-backup script that does the copying to a remote server.
# Run as the STORAGE_USER user, not as root. Pass our settings in
# environment variables so the script has access to STORAGE_ROOT.
post_script = os.path.join(backup_root, 'after-backup')
if os.path.exists(post_script):
shell('check_call',
['su', env['STORAGE_USER'], '-c', post_script],
env=env)
def run_duplicity_verification():
env = load_environment()
backup_root = os.path.join(env["STORAGE_ROOT"], 'backup')
backup_cache_dir = os.path.join(backup_root, 'cache')
backup_dir = os.path.join(backup_root, 'encrypted')
env_with_passphrase = { "PASSPHRASE" : open(os.path.join(backup_root, 'secret_key.txt')).read() }
shell('check_call', [
"/usr/bin/duplicity",
"--verbosity", "info",
"verify",
"--compare-data",
"--archive-dir", backup_cache_dir,
"--exclude", backup_root,
"file://" + backup_dir,
env["STORAGE_ROOT"],
], env_with_passphrase)
if __name__ == "__main__":
import sys
if sys.argv[-1] == "--verify":
# Run duplicity's verification command to check a) the backup files
# are readable, and b) report if they are up to date.
run_duplicity_verification()
else:
# Perform a backup. Add --full to force a full backup rather than
# possibly performing an incremental backup.
full_backup = "--full" in sys.argv
perform_backup(full_backup)