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.
✅ Key Takeaways
- Instance Templates = blueprints for VMs
- Great for scaling, automation, and maintaining identical environments
- Templates are immutable → update via Create Similar
- Always use deterministic configs for reliability
- Supports global, regional, and zonal scoping