AWS Reserved Instances vs On-Demand Explained


AWS Reserved Instances vs On-Demand Explained

AWS Reserved Instances vs. On-Demand:

  • Reserved Instances:
    • Lower cost with long-term commitment.
    • Best for predictable, steady workloads.
    • Offers up to 72% discount compared to On-Demand.
  • On-Demand Instances:
    • Pay-as-you-go, higher flexibility.
    • Ideal for variable, unpredictable workloads.
    • No long-term commitment is required.

AWS Reserved Instances and On-Demand Instances

AWS Reserved Instances vs. On-Demand

In the Amazon Web Services (AWS) realm, two primary instance options stand out for their distinct advantages and use cases: AWS Reserved Instances and On-Demand Instances.

To navigate the AWS ecosystem effectively, it’s crucial to comprehend what each option entails and how they differ fundamentally.

  • AWS Reserved Instances: These are not physical instances but a billing discount for using On-Demand Instances in your account. By committing to a specific instance type in a particular region for a fixed term (usually 1 or 3 years), you receive a significant discount compared to On-Demand pricing.
  • On-Demand Instances: These instances offer maximum flexibility, allowing you to pay by the second for the compute capacity that you use. They are ideal for short-term, irregular workloads where you can’t predict the need.

The fundamental difference between these two lies in their pricing structure and commitment level.

Reserved Instances require a long-term commitment but offer considerable cost savings, while On-Demand Instances provide flexibility without the need for upfront commitment or long-term planning.

Analysis: AWS Reserved Instances vs. On-Demand Instances

AWS Reserved Instances vs. On-Demand Instances

Understanding their pricing models is critical when choosing between AWS Reserved Instances and On-Demand Instances.

This knowledge enables organizations to select the best option with their consumption patterns and budgetary constraints.

Pricing Models:

  • Reserved Instances Pricing:
    • Significant Discount: By committing to a Reserved Instance, you can enjoy up to 72% discount compared to On-Demand pricing​​.
    • Fixed Duration: These discounts apply for the duration of the reservation, providing cost predictability and long-term savings.
  • On-Demand Instances Pricing:
    • Pay-as-You-Go: You pay for On-Demand Instances by the second, offering a flexible pricing model ideal for unpredictable workloads.
    • No Long-Term Commitment: This model requires no upfront payment or long-term commitment, making it suitable for temporary, spiky, or unpredictable workloads.

The choice between these two models hinges on your organizational needs. If you have predictable usage and can commit to a certain level of AWS resource utilization, Reserved Instances may offer significant cost savings.

Conversely, if your workload is variable or you require the flexibility to scale up or down rapidly, On-Demand Instances might be more appropriate.

Financial Implications and Savings

Cost Savings:

The financial advantages of AWS Reserved Instances are a pivotal aspect to consider, especially when contrasted with On-Demand Instances:

  • Significant Discount Opportunities: Reserved Instances can yield substantial cost savings, offering discounts of up to 72% compared to On-Demand instance pricing​​. This can result in considerable financial benefits for long-term, consistent workloads.
  • Long-Term Financial Planning: These savings make Reserved Instances an attractive option for businesses looking to optimize their cloud expenditure over a fixed period, enabling more predictable budgeting and financial planning.

Billing and Discounts:

Understanding the billing mechanism of Reserved Instances clarifies their cost-effectiveness:

  • Not Physical Instances: It’s important to note that Reserved Instances are not physical instances themselves. Instead, they represent a billing discount for using On-Demand Instances in your account​​.
  • Flexible Application: This discount model offers flexibility in applying the savings across your AWS usage, aligning with your varying compute needs while benefiting from reduced costs.

Strategic Considerations for Choosing Between the Two

Strategic Considerations for Choosing Between the Two

Assessing Business Needs:

Choosing the right AWS instance type involves a strategic evaluation of your business requirements:

  • Understand Usage Patterns: Assess whether your workload is consistent, predictable, or fluctuates. Reserved Instances are ideal for predictable, steady workloads, whereas On-Demand Instances suit irregular, fluctuating usage.
  • Consider Commitment and Flexibility: Evaluate your willingness to commit to a long-term contract. If your business can commit, Reserved Instances offer financial benefits. If not, the flexibility of On-Demand Instances might be more suitable.

Capacity Reservation:

Reserved Instances offer another strategic advantage – capacity reservation:

  • Guaranteed Availability: You reserve capacity when you purchase a Reserved Instance in a specific Availability Zone. This ensures that your required resources are available when needed, which is particularly important for critical applications and services.
  • Strategic Resource Allocation: This feature allows businesses to plan and allocate resources strategically, ensuring uninterrupted operations, especially when resource demand is high.

In conclusion, while both Reserved Instances and On-Demand Instances provide robust solutions for different needs, understanding the financial implications, cost savings, and strategic considerations is critical to making an informed choice that aligns with your business objectives and operational demands.

Top 5 Best Practices for Optimal Utilization

When selecting between AWS Reserved Instances and On-Demand Instances, consider these best practices for optimal utilization:

  1. Conduct a Thorough Usage Analysis:
    • Regularly review your AWS usage patterns.
    • Identify trends and predict future needs for more informed decision-making.
  2. Balance Cost and Flexibility:
    • Weigh the cost savings of Reserved Instances against the flexibility of On-Demand Instances.
    • Consider using a mix of both to balance budget constraints with the need for scalability.
  3. Leverage Cost Management Tools:
    • Utilize AWS cost management tools to track and optimize your spending.
    • Regularly review and adjust your instance strategy based on these insights.
  4. Plan for Long-Term Commitments:
    • Evaluate your capacity for long-term commitments before opting for Reserved Instances.
    • Ensure alignment with your business’s strategic goals and financial plans.
  5. Stay Informed About AWS Updates:
    • Keep abreast of new AWS features and pricing models.
    • Regularly reassess your choices in light of these updates to maintain optimal efficiency.


What are AWS Reserved Instances?

Reserved Instances are a billing option that provides a significant discount compared to On-Demand pricing
in exchange for committing to a specific usage (instance type and region) for a one-year or three-year term.

How do Reserved Instances differ from On-Demand Instances?

Reserved Instances offer up to a 72% discount for a long-term commitment, making them best for predictable, steady workloads. On-demand instances provide higher flexibility without needing a long-term commitment, which is ideal for variable, unpredictable workloads.

What are the main benefits of choosing Reserved Instances?

The main benefits include lower costs through significant discounts, budget predictability due to fixed pricing over the term, and capacity reservation when chosen, ensuring your ability to launch instances when needed.

Who should consider using On-Demand Instances?

On-demand instances suit users with short-term, spiky, or unpredictable workloads that cannot be interrupted. They are also ideal for projects being developed or tested on AWS for the first time.

Can I switch from On-Demand to Reserved Instances?

You can switch from On-Demand Instances to Reserved Instances at any time by purchasing a Reserved Instance that matches your desired configuration. This will immediately start providing you with cost-saving benefits for the term.

What types of Reserved Instances are available?

AWS offers three types of Reserved Instances: Standard Reserved Instances (offering the most significant discount but least flexibility), Convertible Reserved Instances (offering lower discounts but more flexibility in terms), and Scheduled Reserved Instances (for use within specific time windows).

How much can I save with Reserved Instances compared to On-Demand?

With Reserved Instances, you can save up to 72% over On-Demand Instance pricing, depending on the term length, payment option, and instance type you choose.

Are there any upfront costs associated with Reserved Instances?

Reserved Instances offer several payment options: All Upfront (highest discount), Partial Upfront (balance between discount and upfront payment), and No Upfront (lower discount but no initial payment).

What happens if my workload changes and I no longer need my Reserved Instance?

If your needs change, AWS offers a Reserved Instance Marketplace where you can sell unused or partially used Reserved Instances to other AWS customers, potentially recouping some of your costs.

Is there a minimum use requirement for Reserved Instances?

When you purchase a Reserved Instance, you commit to paying for the instance over the entire term you select, regardless of how much you use it. This commitment is why the discounts are offered.

How do I decide between Standard and Convertible Reserved Instances?

Choose Standard Reserved Instances if you have steady-state, predictable usage and want the highest possible discount. Opt for Convertible Reserved Instances if you require flexibility to change instance types, operating systems, or tenancies over the term.

Can I use Reserved Instances across multiple AWS regions?

No, Reserved Instances are purchased for a specific region and cannot be transferred to another region. You must buy new Reserved Instances for each region where you want the benefits.

How do On-Demand Instances get billed?

On-demand instances are billed per second or per hour, with no long-term commitment or upfront payment. You pay only for the computing capacity you consume.

What’s the best strategy for combining Reserved and On-Demand Instances?

A common strategy is to use Reserved Instances to cover the base workload with predictable performance requirements and supplement with On-Demand Instances to handle peak loads or temporary increases in demand.

Can I automatically apply Reserved Instance discounts to my running instances?

Yes, AWS automatically applies the cost benefits of Reserved Instances across your running instances that match the specifications (instance type, region, etc.) of the Reserved Instance without any need for manual intervention.


  • Fredrik Filipsson

    Fredrik Filipsson brings two decades of Oracle license management experience, including a nine-year tenure at Oracle and 11 years in Oracle license consulting. His expertise extends across leading IT corporations like IBM, enriching his profile with a broad spectrum of software and cloud projects. Filipsson's proficiency encompasses IBM, SAP, Microsoft, and Salesforce platforms, alongside significant involvement in Microsoft Copilot and AI initiatives, improving organizational efficiency.

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