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Find EC2 Capacity with On-Demand Capacity Reservations

by Craig Cooley

The Problem​

When launching GPU or other high-demand EC2 instance types, you may see InsufficientInstanceCapacity errors when capacity simply isn't available in the Availability Zone you tried. Manually checking each region and AZ one-by-one is time-consuming, especially when you need instances urgently for a customer POC, benchmark, or migration.

The Solution​

FindEC2Capacity_ODCR.ps1 automates the capacity hunt by creating On-Demand Capacity Reservations (ODCRs) across all supported AZs simultaneously. If capacity exists anywhere, the script finds it and reserves it for you - and provides the command to cancel the reservation if needed.

What It Does​

  • Scans all regions and AZs for a given instance type in parallel
  • Creates ODCRs wherever capacity is available
  • Shows on-demand pricing per hour for each successful reservation
  • Lets you choose which reservations to keep — automatically cancels the rest
  • Accumulates capacity over time for scarce instance types (TargetQuantity mode) into an existing ODCR.

Use Cases​

ScenarioMode
Need to quickly find a specific instance type (g6e, p5, etc.) in any regionParallel (default)
Customer needs 10 instances and capacity becomes available over timeTargetQuantity (-TargetQuantity)
Reserving capacity in a specific AZZone mode (-Zone)

Supported Platforms​

  • All EC2 capacity-reservation platforms — Windows, Linux, Ubuntu Pro, Red Hat Enterprise Linux, SUSE Linux, and the SQL Server / RHEL HA variants (matches the AWS API, queried dynamically). Linux is a friendly alias for Linux/UNIX.
  • All EC2 instance types (validated against the AWS Pricing API)
  • All commercially available AWS regions

How to Run​

The recommended environment is AWS CloudShell (PowerShell 7 and AWS modules are pre-installed):

pwsh
.\FindEC2Capacity_ODCR.ps1 -OS Windows -InstanceType g7e.2xlarge -RegionGroup us

⚠️ Billing: You are billed at the on-demand rate from the moment an ODCR is created, even if no instance is running in it. Cancel reservations when done.

Get Started​

📖 Full documentation and examples →

📥 Download FindEC2Capacity_ODCR.ps1