hypervisor/host capabilities (#240)

* hypervisor/host capabilities

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>

* format

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>

* fix

* api note

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>

Author: shwstppr

source/adminguide/hosts.rst

@@ -207,6 +207,23 @@ any system that is not up to date with patches.
 <http://docs.cloudstack.org/Knowledge_Base/Possible_VM_corruption_if_XenServer_Hotfix_is_not_Applied/Highly_Recommended_Hotfixes_for_XenServer_5.6_SP2>`_.
 
 
+Hypervisor Capabilities
+-----------------------
+For different hypervisors and their versions, various capabilities such as maximum number of guest VMs per host, maximum number of volumes per VM, security group support, etc are considered by CloudStack. These capabilities are stored in the **cloud.hypervisor_capabilities** table in the database. If a specific hypervisor version is not available in the database, values against the *default* version for the hypervisor will be used.
+These capabilities can be listed using API - ``listHypervisorCapabilities``. Some of the hypervisor capabilities can also be updated for a hypervisor type and version combination using API - ``updateHypervisorCapabilities``.
+
+Following hypervisor-specific documentations can be referred for different maximums for a particular hypervisor host:
+
+- VMware: `VMware Configuration Maximum tool <https://configmax.vmware.com/guest?vmwareproduct=vSphere&release=vSphere%207.0&categories=1-0,2-0>`_.
+
+- Citrix Hypervisor/Xenserver/XCP-ng: `Configuration limits | Citrix Hypervisor 8.2 <https://docs.citrix.com/en-us/citrix-hypervisor/system-requirements/configuration-limits.html>`_.
+
+
+.. note::
+   Guest VM limit check is not done while deploying a VM on a KVM hypervisor host.
+
+
+
 Changing Host Password
 ----------------------
 
@@ -366,8 +383,8 @@ administrator must set CONFIG\_VIRTIO\_BALLOON=y in the virtio
 configuration.
 
 
-Hypervisor capabilities
-^^^^^^^^^^^^^^^^^^^^^^^
+Hypervisor capability
+^^^^^^^^^^^^^^^^^^^^^
 
 The hypervisor must be capable of using the memory ballooning.