Open Lustre is a full working Lustre filesystem - MGS, MDT, an OST per node, active-active HA with failover - brought up on GCP or Azure with one command. The unconventional part is that the OSTs sit on cloud object storage, not disks.

That is possible because of objbacker.io: a ZFS vdev that writes directly to object storage.

The managed Lustre CSI drivers that GKE and AKS ship for their own managed Lustre services mount this filesystem transparently.