Cannot deploy VM / No Valid Host Was Found

Issue

• Cannot deploy VM. Heat stack creation fails with error No Valid Host was found.

[root@hra-overcloud-controller-0 nova]# grep req-fba6fdf8-0b9a-47c4-957a-c7bcdb23dd78 *
nova-api.log:2017-07-20 02:31:57.100 2804 INFO nova.osapi_compute.wsgi.server [req-fba6fdf8-0b9a-47c4-957a-c7bcdb23dd78 af5818beab53413c83cbe3ff1fe16508 c946c63682c249b495482c62e09eb3d1 - default default] 172.21.30.50 "POST /v2.1/servers HTTP/1.1" status: 202 len: 780 time: 2.4322610
nova-conductor.log:2017-07-20 02:31:57.255 2741 WARNING nova.scheduler.utils [req-fba6fdf8-0b9a-47c4-957a-c7bcdb23dd78 af5818beab53413c83cbe3ff1fe16508 c946c63682c249b495482c62e09eb3d1 - - -] Failed to compute_task_build_instances: No valid host was found. There are not enough hosts available.
nova-conductor.log:2017-07-20 02:31:57.255 2741 WARNING nova.scheduler.utils [req-fba6fdf8-0b9a-47c4-957a-c7bcdb23dd78 af5818beab53413c83cbe3ff1fe16508 c946c63682c249b495482c62e09eb3d1 - - -] [instance: 3b9af6f0-df8e-451d-9aee-8f299934b4f6] Setting instance to ERROR state.