Latest virtnbdbackup version now supports backing up remote libvirt hosts, too. No installation on the hypervisor required anymore:

virtnbdbackup -U qemu+ssh://usr@hypervisor/system -d vm1 -o /backup/vm1

Same applies for restore operations, other enhancements are:

• New backup mode auto which allows easy backup rotation.
• Option to freeze only specific filesystems within backed up domain.
• Remote backup via dedicated network: use --nbd-ip to bind the remote NDB service to an specific interface.
• If virtual machine requires additional files like specific UEFI/Kernel image, these are saved via SFTP from the remote host, too.
• Restore operation can now adjust domain config accordingly (and redefine it if desired).

Next up: add TLS support for remote NBD connections.