Show host usage statistics

List the hosts and the nova-related services that run on them:

$ nova host-list
+-----------+-------------+----------+
| host_name | service     | zone     |
+-----------+-------------+----------+
| devstack  | conductor   | internal |
| devstack  | compute     | nova     |
| devstack  | cert        | internal |
| devstack  | network     | internal |
| devstack  | scheduler   | internal |
| devstack  | consoleauth | internal |
+-----------+-------------+----------+

Get a summary of resource usage of all of the instances running on the host:

$ nova host-describe devstack
 +-----------+----------------------------------+-----+-----------+---------+
| HOST     | PROJECT                          | cpu | memory_mb | disk_gb |
+----------+----------------------------------+-----+-----------+---------+
| devstack | (total)                          | 2   | 4003      | 157     |
| devstack | (used_now)                       | 3   | 5120      | 40      |
| devstack | (used_max)                       | 3   | 4608      | 40      |
| devstack | b70d90d65e464582b6b2161cf3603ced | 1   | 512       | 0       |
| devstack | 66265572db174a7aa66eba661f58eb9e | 2   | 4096      | 40      |
+----------+----------------------------------+-----+-----------+---------+

The cpu column shows the sum of the virtual CPUs for instances running on the host.

The memory_mb column shows the sum of the memory (in MB) allocated to the instances that run on the host.

The disk_gb column shows the sum of the root and ephemeral disk sizes (in GB) of the instances that run on the host.

The row that has the value used_now in the PROJECT column shows the sum of the resources allocated to the instances that run on the host, plus the resources allocated to the virtual machine of the host itself.

The row that has the value used_max row in the PROJECT column shows the sum of the resources allocated to the instances that run on the host.