Citrix XenServer and XCP-ng monitoring via the XAPI management API (read-only special agent, no agent on the hypervisors) — pool members and HA, alerts, storage repositories (capacity, I/O, attach state, multipath), plus piggyback data per hypervisor host (CPU, memory, interfaces, license, updates, certificates) and per VM (power state, CPU, memory, disks, NICs, snapshots, guest tools).