WireGuard and lsyncd to sync a directory.

install wireguard

apt install wireguard / pacman install wireguard-tools

generate keypairs

wg genkey | tee server_private.key | wg pubkey > server_public.key

Server config file /etc/wireguard/wg0.conf

[Interface]
PrivateKey = <server_private_key>
Address = 10.11.12.1/24
ListenPort = 51820

[Peer]
PublicKey = <client1_public_key>
AllowedIPs = 10.11.12.2/32

[Peer]
PublicKey = <client2_public_key>
AllowedIPs = 10.11.12.3/32

# Repeat for all clients...

Enable wireguard in systemd

sudo systemctl enable wg-quick@wg0.service
sudo systemctl daemon-reload

Server iptables

sudo iptables -A FORWARD -o wg0 -j ACCEPT
sudo iptables -t nat -A POSTROUTING -s 10.11.12.0/24 -o eth0 -j MASQUERADE
sudo iptables -A PREROUTING -p tcp -m tcp --dport 2222 -j DNAT --to-destination 10.11.12.x:22
sudo iptables -A POSTROUTING -d 10.11.12.X/22 -p tcp -m tcp --dport 22 -j MASQUERADE
sudo iptables -A INPUT -i wg0 -j ACCEPT
sudo iptables -A FORWARD -i wg0 -j ACCEPT
sudo iptables -A OUTPUT -o wg0 -j ACCEPT

Client iptables 

Client config

[Interface]
PrivateKey =
Address = 10.11.12.3/24  # Unique IP for each client, e.g., 10.11.12.2, 10.11.12.3, etc.

[Peer]
PublicKey =
Endpoint = hostname:51820
AllowedIPs = 10.11.12.0/24  # Route only traffic destined for the VPN subnet through WireGuard
PersistentKeepalive = 25

On both server and client

/etc/syssctl.conf

net.ipv4.ip_forward=1


sudo sysctl -p

lsyncd config on server /etc/lsyncd/lsyncd.conf.lua

settings {
    logfile    = "/var/log/lsyncd/lsyncd.log",
    statusFile = "/var/log/lsyncd/lsyncd.status",
    insist = true,
}

sync {
    default.rsyncssh,
    source = "/home/v3d/fubomatic/media/events/failsafe",
    host = "limiteduser@10.11.12.3",
    targetdir = "/home/limiteduser/apply.fubar.space-backup/",
    delay = 2,
    rsync = {
        archive = true,
        compress = true,
        _extra = {"--delete"}
    },
    ssh = {
        port = 22,
        identityFile = "/root/.ssh/limited-user"
    }
}