mailinabox/management/backup.py

#!/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 backup is made using duplicity into the
#    directory STORAGE_ROOT/backup/duplicity.
# 3) The stopped services are restarted.
# 4) The backup files are encrypted with a long password (stored in
#    backup/secret_key.txt) to STORAGE_ROOT/backup/encrypted.
# 5) STORAGE_ROOT/backup/after-backup is executd if it exists.

import sys, os, os.path, shutil, glob

from utils import exclusive_process, load_environment, shell

# settings
full_backup = "--full" in sys.argv
keep_backups_for = "31D" # destroy backups older than 31 days except the most recent full backup

env = load_environment()

exclusive_process("backup")

# Ensure the backup directory exists.
backup_dir = os.path.join(env["STORAGE_ROOT"], 'backup')
backup_duplicity_dir = os.path.join(backup_dir, 'duplicity')
os.makedirs(backup_duplicity_dir, exist_ok=True)

# On the first run, always do a full backup. Incremental
# will fail.
if len(os.listdir(backup_duplicity_dir)) == 0:
	full_backup = True
else:
	# When the size of incremental backups exceeds the size of existing
	# full backups, take a new full backup. We want to avoid full backups
	# because they are costly to synchronize off-site.
	full_sz = sum(os.path.getsize(f) for f in glob.glob(backup_duplicity_dir + '/*-full.*'))
	inc_sz = sum(os.path.getsize(f) for f in glob.glob(backup_duplicity_dir + '/*-inc.*'))
	# (n.b. not counting size of new-signatures files because they are relatively small)
	if inc_sz > full_sz * 1.5:
		full_backup = True

# Stop services.
shell('check_call', ["/usr/sbin/service", "dovecot", "stop"])
shell('check_call', ["/usr/sbin/service", "postfix", "stop"])

# 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",
		"--no-encryption",
		"--archive-dir", "/tmp/duplicity-archive-dir",
		"--name", "mailinabox",
		"--exclude", backup_dir,
		"--volsize", "100",
		"--verbosity", "warning",
		env["STORAGE_ROOT"],
		"file://" + backup_duplicity_dir
		])
finally:
	# Start services again.
	shell('check_call', ["/usr/sbin/service", "dovecot", "start"])
	shell('check_call', ["/usr/sbin/service", "postfix", "start"])

# Remove old backups. This deletes all backup data no longer needed
# from more than 31 days ago. Must do this before destroying the
# cache directory or else this command will re-create it.
shell('check_call', [
	"/usr/bin/duplicity",
	"remove-older-than",
	keep_backups_for,
	"--archive-dir", "/tmp/duplicity-archive-dir",
	"--name", "mailinabox",
	"--force",
	"--verbosity", "warning",
	"file://" + backup_duplicity_dir
	])

# Remove duplicity's cache directory because it's redundant with our backup directory.
shutil.rmtree("/tmp/duplicity-archive-dir")

# Encrypt all of the new files.
backup_encrypted_dir = os.path.join(backup_dir, 'encrypted')
os.makedirs(backup_encrypted_dir, exist_ok=True)
for fn in os.listdir(backup_duplicity_dir):
	fn2 = os.path.join(backup_encrypted_dir, fn) + ".enc"
	if os.path.exists(fn2): continue

	# Encrypt the backup using the backup private key.
	shell('check_call', [
		"/usr/bin/openssl",
		"enc",
		"-aes-256-cbc",
		"-a",
		"-salt",
		"-in", os.path.join(backup_duplicity_dir, fn),
		"-out", fn2,
		"-pass", "file:%s" % os.path.join(backup_dir, "secret_key.txt"),
		])

	# The backup can be decrypted with:
	# openssl enc -d -aes-256-cbc -a -in latest.tgz.enc -out /dev/stdout -pass file:secret_key.txt | tar -z

# Remove encrypted backups that are no longer needed.
for fn in os.listdir(backup_encrypted_dir):
	fn2 = os.path.join(backup_duplicity_dir, fn.replace(".enc", ""))
	if os.path.exists(fn2): continue
	os.unlink(os.path.join(backup_encrypted_dir, fn))

# 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_dir, 'after-backup')
if os.path.exists(post_script):
	shell('check_call',
		['su', env['STORAGE_USER'], '-c', post_script],
		env=env)