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, boot disk image or container image, zone, labels, and other instance properties. You can then use an instance template to create a managed instance group or to create individual 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.
Instance templates are designed to create instances with identical configurations. So it is not possible to update an existing instance template or change an instance template after it has been created. If an instance template goes out of date, or you need to make changes to the configuration, create a new instance template. You can also override instance template fields when creating a VM instance from an instance template.
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.
Please note that labels defined within an instance template are applied to all instances that will be created from that instance template. The labels do not apply to the instance template itself.
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.