Reserved Instances

What Are Reserved Instances?

Reserved Instances (RIs) are a pricing model from major cloud providers where you reserve compute capacity in advance for a fixed period – typically 1 or 3 years. In return, you receive significant discounts compared to regular on-demand prices. With AWS, savings can reach up to 72% depending on configuration and upfront payment.

Pricing Models Compared

On-Demand

You pay per hour or second without long-term commitment. Maximum flexibility but the most expensive tier. Ideal for unpredictable or short-term workloads.

Reserved Instances

Reservation for 1 or 3 years with significant discounts. Three payment options: All Upfront (highest discount), Partial Upfront (medium discount), and No Upfront (lowest discount but no prepayment). Ideal for stable, predictable base workloads.

Savings Plans

AWS Savings Plans are a more flexible alternative to RIs. You commit to a certain hourly spend level (e.g., $10/hour), receive discounts in return, and retain the flexibility to change instance types and regions. Savings Plans also apply to Fargate and Lambda.

Strategies for Reserved Instances

Coverage Analysis

Before purchasing Reserved Instances, analyze your actual usage over at least 30 days. AWS Cost Explorer shows usage patterns and recommends optimal RI configurations. Only reserve capacity you use consistently – typically the baseline of your utilization.

Mixed Strategy

The optimal strategy combines different pricing models: Reserved Instances for stable base load (60-70% of capacity), Spot Instances for fault-tolerant batch workloads, and On-Demand for peak loads. This mix maximizes savings while maintaining flexibility.

Reserved Instances Across Providers

• AWS: Standard RIs (instance type-bound) and Convertible RIs (changeable). Plus Savings Plans as a more flexible alternative.
• Azure: Azure Reservations for VMs, SQL Database, Cosmos DB, and more. 1- or 3-year terms with up to 72% discount.
• GCP: Committed Use Discounts (CUDs) for 1 or 3 years. Automatic discount for resource-based CUDs without specific instance binding.

Pitfalls with Reserved Instances

The biggest mistake is over-commitment: purchasing too many RIs that remain unused. Avoid 3-year commitments if your workloads might change significantly. Regularly check RI utilization and use the AWS RI Marketplace to resell unneeded RIs.

Reserved Instances for Mid-Market Companies

For mid-market companies, Reserved Instances are an effective lever for cloud cost optimization. Start with a 1-year reservation for your most stable workloads – typically databases and base infrastructure. Use AWS Cost Explorer or tools like CloudHealth for analysis. Even 30-40% RI coverage can reduce the monthly cloud bill by 20-30%.