An instance template is an API resource that you can use to create VM instances and managed instance groups. Instance templates define the machine type, image, zone, and other instance properties. You can then use an instance template to create a managed instance group or to create individual standalone VM instances. Instance templates are a convenient way to save a VM instance's configuration so you can use it later to create new VM instances or groups of VM instances.
An instance template is a global resource that is not bound to a zone or a
region. However, you will specify some zonal resources in an instance
template, which restricts the template to the zone where that resource resides.
For example, if you include a read-only persistent disk from
your instance template, you cannot use that template in any other zone because
that specific disk exists only in zone
us-central1-b. For more information
about zonal resources, read Regions and Zones.
To learn how to create an instance template, read Creating Instance Templates.
When to use instance templates
You can use instance templates any time you want to quickly create VM instances based off of a preexisting configuration. If you want to create a group of identical instances, you must use an instance template to create a managed instance group.