Reserve compute node resources (#239)

Closes osism/issues#799

Signed-off-by: Christian Berendt <berendt@osism.tech>

Author: berendt

docs/guides/configuration-guide/openstack/nova.md

@@ -27,3 +27,26 @@ cat /sys/module/kvm_intel/parameters/nested
 Y
 docker restart nova_libvirt
 ```
+
+## Reserve compute node resources
+
+How many resources you want to reserve on a compute node depends very much on which additional
+services are running on the compute node.
+
+### Host memory
+
+* https://docs.openstack.org/nova/latest/configuration/config.html#DEFAULT.reserved_host_memory_mb
+
+```ini title="environments/kolla/files/overlays/nova/nova-compute.conf"
+[DEFAULT]
+reserved_host_memory_mb = 32768
+```
+
+### Host CPUs
+
+* https://docs.openstack.org/nova/latest/configuration/config.html#DEFAULT.reserved_host_cpus
+
+```ini title="environments/kolla/files/overlays/nova/nova-compute.conf"
+[DEFAULT]
+reserved_host_cpus = 4
+```