Part-10: 🚀 Google Cloud Compute Engine – Instance Templates Explained (GCP)

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When working with Google Cloud Compute Engine, managing multiple VM instances with consistent configurations can become repetitive. That’s where Instance Templates come into play.

🔹 What is an Instance Template?

An Instance Template is a reusable configuration resource in Google Cloud that you can use to quickly:

Create VM Instances
Create Managed Instance Groups (MIGs) (covered later)
Create VM reservations (future or immediate)

Essentially, Instance Templates store VM configuration details such as:

Machine configuration (CPU, Memory)
Boot Disk or Container Image
Identity & API Access
Firewall settings
Networking & Sole-Tenancy options
Management, Security, and Disk settings

🔹 Why use Instance Templates?

To create VMs with identical configurations
To define your VM setup once and reuse it across multiple deployments
To ensure consistency, repeatability, and automation when scaling

🔹 Updating Instance Templates

⚠️ You cannot update an existing Instance Template.
Instead:

Use “Create Similar” to clone an existing template
Add/modify the new settings in the cloned template

🔹 Overriding Configurations

When creating a VM using an Instance Template, you can still override certain configurations (e.g., disk size, metadata).

🔹 Ways to Create Instance Templates

From scratch – manually defining all configs
From existing template – using Create Similar option
From existing VM instance – possible only via gcloud CLI or API (not via Console)

🔹 Deterministic Instance Templates

Best practice: make your templates deterministic.
👉 Be explicit about versions in startup scripts (e.g., install nginx=1.18.0 instead of just nginx).
This prevents unexpected behavior due to version changes in third-party software.

🔹 Regional vs Global Templates

You can create regional or global Instance Templates.
But note:

If a zonal resource (like a persistent disk) is used in a global/regional template, the template becomes restricted to that zone.
If a regional resource is used in a global template, it gets restricted to that region.