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-containers

# Array of containers to synchronize

declare -A SYNCCONT
declare -A SYNCCONTDETAIL

# sample container 1
SYNCCONTDETAIL["lxcremote"]='srcserver'
SYNCCONTDETAIL["sshcmd"]='ssh -p2222 -oStrictHostKeyChecking=no root@srcserver'
string=$(declare -p SYNCCONTDETAIL)
SYNCCONT['samplecont1']=${string}

# sample container 2
SYNCCONTDETAIL["lxcremote"]='srcserver'
SYNCCONTDETAIL["sshcmd"]='ssh -p2222 -oStrictHostKeyChecking=no root@srcserver'
string=$(declare -p SYNCCONTDETAIL)
SYNCCONT['samplecont2']=${string}

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 needs 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, [email protected], 2021-02-23

set -e
# set -x

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

. "$DIR/lxc-sync-config"
. "$DIR/lxc-sync-containers"

function localtargetexists {

	local CONTNAME=$1

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

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

function initsync {

	local CONTNAME=$1
	local LXCREMOTE=$2
	local SSHCMD=$3

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

function incrementalsync {

	local CONTNAME=$1
	local LXCREMOTE=$2
	local SSHCMD=$3

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

for CONTNAME in "${!SYNCCONT[@]}"; do

	eval "${SYNCCONT["$CONTNAME"]}"
	
	set +e
	localtargetexists $CONTNAME
	CONTEXISTS=$?
	set -e
	if [ $CONTEXISTS == 0 ]; then
		initsync "$CONTNAME" "${SYNCCONTDETAIL['lxcremote']}" "${SYNCCONTDETAIL['sshcmd']}"
	else
		incrementalsync "$CONTNAME" "${SYNCCONTDETAIL['lxcremote']}" "${SYNCCONTDETAIL['sshcmd']}"
	fi

done