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Reserved Instances (RIs) in AWS offer significant cost savings compared to On-Demand instances. Understanding how to calculate these savings helps optimize cloud expenses and improve budgeting strategies.
Understanding Reserved Instances
Reserved Instances are a billing discount applied to Amazon EC2 instances when you commit to a consistent usage level over a period, typically one or three years. They provide a lower hourly rate in exchange for this commitment.
Calculating Savings
The basic formula to estimate savings involves comparing the cost of On-Demand instances with Reserved Instances. The calculation considers the hourly rates and the total hours in the reservation period.
Practical Calculation Example
Suppose an On-Demand EC2 instance costs $0.10 per hour. A 1-year Reserved Instance offers a discounted rate of $0.06 per hour. To calculate the savings:
- Calculate total On-Demand cost: $0.10 x 8760 hours = $876
- Calculate total RI cost: $0.06 x 8760 hours = $525.60
- Determine savings: $876 – $525.60 = $350.40
This example shows a savings of approximately 40% over the year.