Update documentation for strict host tags

Author: vishesh92

source/adminguide/host_and_storage_tags.rst

@@ -49,6 +49,35 @@ To explain the behavior of host tags, some examples will be demonstrated with tw
     * Offering: h3
     None of the hosts have compatible tags and it will not be possible to deploy a VM with the offering. However, CloudStack ignores this behavior when a host is manually selected.
 
+.. _strict-host-tags:
+Strict Host Tags
+-----------------
+During certain operations, such as VM deployment, changing compute offering and live migration,
+CloudStack will ignore the host tags if a host is specified. This can result in issues in which
+a VM is deployed on an undesired host.
+
+This behavior can be changed by setting the `vm.strict.host.tags` to the list of tags which
+should match with the host. While performing the operations where a mismatch of tags can occur,
+CloudStack will fail the operation if the host tags do not match with the tags specified
+in `vm.strict.host.tags`.
+
+If `resource.limit.host.tags` is defined and `vm.strict.resource.limit.host.tag.check` is set to
+`true`, the host tags will be checked against the tags specified in `vm.strict.host.tags` as
+well as the `resource.limit.host.tags`.
+
+.. list-table:: Strict host tags related global settings
+   :header-rows: 1
+
+   * - Parameter
+     - Default
+     - Description
+   * - ``vm.strict.host.tags``
+     - empty
+     - A comma-separated list of tags for strict host checking while performing operations like VM deployment, changing compute offering, and live migration.
+   * - ``vm.strict.resource.limit.host.tag.check``
+     - `true`
+     - If set to true, `resource.limit.host.tags` are also included in the strict host tag check.
+
 Storage tags
 ------------
 Storage tags are responsible for directing volumes to compatible primary storage. They are validated with the storage tags entered in the disk offerings or system offerings.

source/adminguide/virtual_machines.rst

@@ -276,6 +276,12 @@ CloudStack's database.  The reboot process does not do this.
 
 When starting an Instance, admin Users have the option to specify a pod, cluster, or host.
 
+.. note::
+   If a host is specified while starting an Instance, the Instance will be deployed on the
+   specified host even if the host's tags do not match the Instance's tags. This can lead to
+   a mismatch of VM's tags with the host's tags which might be undesirable.
+
+   For more details on how to prevent this, see :ref:`strict-host-tags`.
 
 Deleting Instance
 ------------------
@@ -441,6 +447,10 @@ Instance, you can change the Instance's compute offering.
 
 #. Click OK.
 
+.. note::
+   It's possible to have a mismatch of host tags on changing the service offering which might be undesirable.
+
+   For more details on how to prevent this, see :ref:`strict-host-tags`.
 
 .. _cpu-and-memory-scaling:
 
@@ -637,6 +647,11 @@ To manually live migrate an Instance
 
       where i in [0,..,N] and N = number of volumes of the Instance
 
+.. note::
+   There can be a mismatch of VM's tags with the destination host's tags which might be undesirable.
+
+   For more details on how to prevent this, see :ref:`strict-host-tags`.
+
 Moving Instance's Volumes Between Storage Pools (offline volume Migration)
 --------------------------------------------------------------------------