Instance Templates & Groups

Instance templates and instance groups are foundational building blocks for scalable, resilient architectures on Compute Engine. Instance templates define a VM configuration that can be reused, while instance groups manage collections of VM instances as a single unit.

---

Instance Templates

An instance template is a resource that defines the properties of a VM instance — machine type, boot disk image, network configuration, labels, metadata, service account, and more. Templates are immutable — once created, they cannot be modified. To change a configuration, you create a new template.

Creating an Instance Template

gcloud compute instance-templates create web-template-v1 \
  --machine-type=e2-standard-2 \
  --image-family=debian-12 \
  --image-project=debian-cloud \
  --boot-disk-size=20GB \
  --boot-disk-type=pd-balanced \
  --tags=http-server,https-server \
  --metadata=startup-script='#!/bin/bash
apt-get update && apt-get install -y nginx' \
  --service-account=web-sa@my-project.iam.gserviceaccount.com \
  --scopes=cloud-platform \
  --labels=app=web,env=production

Key Properties of Instance Templates

Property	Description
Immutable	Cannot be edited after creation — create a new version instead
Global resource	Not tied to a specific zone or region
Reusable	Can be used by multiple instance groups
Versionable	Use a naming convention like web-template-v1, web-template-v2
No cost	Templates themselves are free — you only pay for VMs created from them

Regional Instance Templates

Regional instance templates restrict usage to a specific region and can reference regional resources (e.g., regional disks, subnet):

gcloud compute instance-templates create web-template-regional \
  --region=europe-west2 \
  --machine-type=e2-standard-2 \
  --image-family=debian-12 \
  --image-project=debian-cloud \
  --subnet=projects/my-project/regions/europe-west2/subnetworks/web-subnet

---

Instance Groups Overview

An instance group is a collection of VM instances that are managed as a single entity. There are two types:

Type	Description
Managed Instance Group (MIG)	Automatically creates and manages identical VMs from an instance template
Unmanaged Instance Group	A collection of heterogeneous existing VMs grouped for load balancing

Managed instance groups are the recommended approach for most production workloads because they provide autoscaling, autohealing, rolling updates, and integration with load balancers.

---

Unmanaged Instance Groups

Unmanaged instance groups are simply a way to group existing VMs for use with a load balancer. They do not provide autoscaling, autohealing, or rolling updates. Each VM can have a different machine type, image, and configuration.

# Create an unmanaged instance group
gcloud compute instance-groups unmanaged create legacy-group \
  --zone=europe-west2-a