Backup
Community / single-node: back up Postgres with your usual tool (pg_dump, snapshots). Include /etc/lattice/entitlement.json.
Paid HA: lattice backup now (sidecar on the leader). Restore is a new cluster (lattice backup restore --from …), then cut relays and the VIP. That is also the DR DC path. Do not stretch the three HA VMs across DCs. See HA — Active / passive DC.
Add a node (paid)
Extra DHCP or DNS after the control plane exists:
lattice-install --mode dhcp-only --peer <primary-ip> --token JOIN
Relays at that site point at this VM, not the VIP. Pools do not move. Community has no extra nodes.