lxc copy --refresh workaround: efficient incremental ZFS snapshot sync with send/receive

lxc-sync-config

LXCBIN=/snap/bin/lxc
LXDBIN=/snap/bin/lxd
ZFSBIN=/sbin/zfs

SYNCSNAPNAME=bsync
LASTSYNCSNAPNAME=bsync-last

ZFSROOT=tank/containers/
MOUNTROOT=/var/snap/lxd/common/lxd/storage-pools/

lxc-sync-README

# This cronjob is configured on the target server:
# - srclxdremotename: name of the lxd remote that contains the container to be synced
# - srclxdcontainername: name of the remote lxd container to be synced
# - locallxdcontainertargetname: local target container name to sync to
# - root@srcserver: ssh root login to the remote lxd server

# lxc-sync jobs
25 12,18 * * * /opt/lxc-sync/lxc-sync.sh -o srclxdremotename -r srclxdcontainername -l locallxdcontainertargetname -c "ssh -p2222 -oStrictHostKeyChecking=no root@srcserver"

lxc-sync.sh

#!/bin/bash

# This script is meant to run on the sync target server that syncs remote container snapshots to local;
# remote and local containers may be running; a remote container is snapshotted and this
# snapshot will be restored on the local receiving container.
#
# IMPORTANT:
# - in the local lxc configuration all remotes need to be configured (see `lxc remote list`)
# - ssh access to the remote/source servers needs to be available to execute remote zfs send
#
# Florian Sager, sager@agitos.de, 2021-02-23

set -e
# set -x

DIR="${BASH_SOURCE%/*}"
if [[ ! -d "$DIR" ]]; then DIR="$PWD"; fi

PROG=${0##*/}

# load local system specific sync config
. "$DIR/lxc-sync-config"

# cron sample:
# 45 12,18 * * * /root/tools/lxc-sync.sh -o host01 -r mycontainer -l mycontainer-standby -c "ssh -p2222 -oStrictHostKeyChecking=no root@host01.dom.tld"

function usage {
cat <<EOF
usage: $PROG [options]
$PROG will sync a ZFS based LXD container from a remote origin server to a local target container.
 
  Options:
    -h    print this help message
    -o    remote origin host according to the name in 'lxc remote list', e.g. "host01"
    -r    remote origin container name, e.g. "mycontainer"
    -l    local target container in LXD syntax, e.g. "mycontainer-standby"
    -c    ssh command to connect to origin server, e.g. "ssh -p2222 -oStrictHostKeyChecking=no root@host01.dom.tld"
EOF
}

function localtargetexists {

	local CONTNAME=$1

	$LXCBIN info $CONTNAME > /dev/null
	RETVAL=$?

	return $([ "$RETVAL" == 0 ] && echo 1 || echo 0)
}

function initsync {

	local LOCALCONTNAME=$1
	local LXCREMOTE=$2
	local REMOTECONTNAME=$3
	local SSHCMD=$4

	$LXCBIN snapshot $LXCREMOTE:$REMOTECONTNAME $SYNCSNAPNAME
	$LXCBIN copy $LXCREMOTE:$REMOTECONTNAME/$SYNCSNAPNAME $LOCALCONTNAME
	$LXCBIN snapshot $LOCALCONTNAME $SYNCSNAPNAME
	$ZFSBIN destroy -r $ZFSROOT$LOCALCONTNAME
	$ZFSBIN create -o mountpoint=$MOUNTROOT$ZFSROOT$LOCALCONTNAME $ZFSROOT$LOCALCONTNAME
	$SSHCMD $ZFSBIN send -c -L $ZFSROOT$REMOTECONTNAME@snapshot-$SYNCSNAPNAME | $ZFSBIN receive -Fu $ZFSROOT$LOCALCONTNAME
}

function incrementalsync {

	local LOCALCONTNAME=$1
	local LXCREMOTE=$2
	local REMOTECONTNAME=$3
	local SSHCMD=$4
	
	set +e
	$LXCBIN delete $LXCREMOTE:$LOCALCONTNAME/$LASTSYNCSNAPNAME
	set -e
	$LXCBIN rename $LXCREMOTE:$REMOTECONTNAME/$SYNCSNAPNAME $LXCREMOTE:$REMOTECONTNAME/$LASTSYNCSNAPNAME
	$LXCBIN snapshot $LXCREMOTE:$REMOTECONTNAME $SYNCSNAPNAME
	$ZFSBIN rename $ZFSROOT$LOCALCONTNAME@snapshot-$SYNCSNAPNAME $ZFSROOT$LOCALCONTNAME@snapshot-$LASTSYNCSNAPNAME
	$SSHCMD $ZFSBIN send -c -L -i $ZFSROOT$REMOTECONTNAME@snapshot-$LASTSYNCSNAPNAME $ZFSROOT$REMOTECONTNAME@snapshot-$SYNCSNAPNAME | $ZFSBIN receive -Fu $ZFSROOT$LOCALCONTNAME
	$ZFSBIN destroy $ZFSROOT$LOCALCONTNAME@snapshot-$LASTSYNCSNAPNAME
	$LXCBIN restore $LOCALCONTNAME $SYNCSNAPNAME
	$LXDBIN sql global "UPDATE instances_snapshots SET creation_date=datetime('now') WHERE instance_id=(SELECT id FROM instances WHERE name='$LOCALCONTNAME') AND name='$SYNCSNAPNAME';" > /dev/null
}

if [ "$#" == "0" ]; then
	usage;
	exit 1;
fi

# read arguments
while getopts o:r:l:c:h option; do
	case "${option}" in
		o) LXCREMOTE=${OPTARG};;
		r) REMOTECONTNAME=${OPTARG};;
		l) LOCALCONTNAME=${OPTARG};;
		c) SSHCMD=${OPTARG};;
		h) usage; exit 1;;
	esac
done

if [ -z "$LXCREMOTE" ] ; then
        echo 'Missing parameter -o' >&2
        exit 3;
fi

if [ -z "$REMOTECONTNAME" ] ; then
        echo 'Missing parameter -r' >&2
        exit 4;
fi

if [ -z "$LOCALCONTNAME" ] ; then
        echo 'Missing parameter -l' >&2
        exit 5;
fi

if [ -z "$SSHCMD" ] ; then
        echo 'Missing parameter -c' >&2
        exit 6;
fi

set +e
localtargetexists $LOCALCONTNAME
LOCALCONTEXISTS=$?
set -e
if [ $LOCALCONTEXISTS == 0 ]; then
	initsync "$LOCALCONTNAME" "$LXCREMOTE" "$REMOTECONTNAME" "$SSHCMD"
else
	incrementalsync "$LOCALCONTNAME" "$LXCREMOTE" "$REMOTECONTNAME" "$SSHCMD"
fi