Compute nodes down, but instances running

Issue

• The three compute nodes of our enviroment, lists as down in the dashboard and in the CLI as well. but the instances are still running fine:

(overcloud) [stack@director ~]$ openstack hypervisor list
+----+----------------------------------+-----------------+--------------+-------+
| ID | Hypervisor Hostname              | Hypervisor Type | Host IP      | State |
+----+----------------------------------+-----------------+--------------+-------+
|  2 | overcloud-compute-1.localdomain   | QEMU            | 10.10.10.10 | down  |
|  5 | overcloud-compute-0.localdomain   | QEMU            | 10.10.10.11 | down  |
|  8 | overcloud-computehp-0.localdomain | QEMU            | 10.10.10.12 | down  |
+----+----------------------------------+-----------------+--------------+-------+