Use the nova host-list command to list the hosts and the nova-related services that are running on them:
$ nova host-list +------------------+-------------+ | host_name | service | +------------------+-------------+ | c2-compute-01 | compute | | c2-compute-01 | network | | c2-compute-02 | compute | | c2-compute-02 | network | | c2-compute-03 | compute | | c2-compute-03 | network | | c2-compute-04 | compute | | c2-compute-04 | network | | c2-controller-01 | cert | | c2-controller-01 | consoleauth | | c2-controller-01 | scheduler | +------------------+-------------+
Use the nova host-describe command to retrieve a summary of resource usage of all of the instances running on the host. The "cpu" column is the sum of the virtual CPUs of all of the instances running on the host, the "memory_mb" column is the sum of the memory (in MB) allocated to the instances running on the hosts, and the "disk_gb" column is the sum of the root and ephemeral disk sizes (in GB) of the instances running on the hosts.
Note that these values are computed using only information about the flavors of the instances running on the hosts. This command does not query the CPU usage, memory usage, or hard disk usage of the physical host.
$ nova host-describe c2-compute-01
+---------------+----------------------------------+-----+-----------+---------+
| HOST | PROJECT | cpu | memory_mb | disk_gb |
+---------------+----------------------------------+-----+-----------+---------+
| c2-compute-01 | (total) | 24 | 96677 | 492 |
| c2-compute-01 | (used_max) | 2 | 2560 | 0 |
| c2-compute-01 | (used_now) | 4 | 7168 | 0 |
| c2-compute-01 | f34d8f7170034280a42f6318d1a4af34 | 2 | 2560 | 0 |
+---------------+----------------------------------+-----+-----------+---------+