Capacity Reservations in AWS are a feature that allows you to reserve compute capacity for Amazon EC2 instances in a specific Availability Zone for any duration. This ensures that you have access to EC2 capacity when you need it, providing a safety net for your mission-critical workloads.
Key aspe…Capacity Reservations in AWS are a feature that allows you to reserve compute capacity for Amazon EC2 instances in a specific Availability Zone for any duration. This ensures that you have access to EC2 capacity when you need it, providing a safety net for your mission-critical workloads.
Key aspects of Capacity Reservations include:
**How It Works:**
When you create a Capacity Reservation, you specify the Availability Zone, instance type, platform (Linux/Windows), and the number of instances you need. AWS then reserves that capacity for your exclusive use until you cancel the reservation.
**Billing Considerations:**
You are billed at the On-Demand rate for the reserved capacity whether or not you run instances. This means you pay for the capacity regardless of utilization. However, when you do launch instances that match your reservation attributes, those instances run at no additional charge since you are already paying for the capacity.
**Flexibility:**
Unlike Reserved Instances, Capacity Reservations do not require a one or three-year commitment. You can create and cancel them as needed, offering greater flexibility for variable workloads or short-term projects.
**Use Cases:**
- Disaster recovery scenarios requiring guaranteed capacity
- Business-critical applications that cannot tolerate capacity constraints
- Events or launches requiring predictable scaling
- Regulatory compliance requiring dedicated capacity
**Combining with Savings Plans:**
You can combine Capacity Reservations with Savings Plans or Regional Reserved Instances to optimize costs while maintaining capacity guarantees. This approach provides both the pricing benefits of long-term commitments and the capacity assurance of reservations.
**Regional vs. Zonal:**
Capacity Reservations are zonal, meaning they guarantee capacity in a specific Availability Zone, unlike Regional Reserved Instances which provide pricing benefits across all zones in a region but do not guarantee capacity.
Capacity Reservations are a feature in Amazon EC2 that allows you to reserve compute capacity for your EC2 instances in a specific Availability Zone. This ensures that you have the capacity you need when you need it, regardless of demand fluctuations in the AWS cloud.
Why are Capacity Reservations Important?
• Guaranteed Capacity: They ensure your applications have access to EC2 capacity when required, which is critical for mission-critical workloads. • Disaster Recovery: Essential for business continuity planning where you must launch instances during failover scenarios. • Compliance Requirements: Some organizations require guaranteed capacity for regulatory or compliance reasons. • Event-Based Scaling: Useful when you anticipate high demand during specific events or peak periods.
How Capacity Reservations Work
1. Create a Reservation: You specify the Availability Zone, instance type, platform (Linux/Windows), and the number of instances.
2. Billing: You are billed for the reserved capacity whether or not you run instances. The billing rate is equivalent to On-Demand pricing.
3. No Commitment: Unlike Reserved Instances, Capacity Reservations have no term commitment. You can create or cancel them at any time.
4. Combine with Savings Plans: You can combine Capacity Reservations with Savings Plans or Regional Reserved Instances to get both capacity assurance and cost savings.
Key Characteristics: • Availability Zone specific • No term commitment required • Can be created and cancelled anytime • Charged at On-Demand rates • Does not provide billing discounts on its own
Exam Tips: Answering Questions on Capacity Reservations
Tip 1: Remember that Capacity Reservations guarantee capacity but do not provide cost savings by themselves. If a question asks about both capacity guarantee AND savings, look for answers combining Capacity Reservations with Savings Plans or Reserved Instances.
Tip 2: Capacity Reservations are Availability Zone specific. If a question mentions needing capacity in a particular AZ, Capacity Reservations is likely the answer.
Tip 3: Unlike Reserved Instances, there is no 1-year or 3-year commitment with Capacity Reservations. They offer flexibility to create and cancel as needed.
Tip 4: When questions mention scenarios like disaster recovery, planned events, or mission-critical applications requiring guaranteed compute resources, think Capacity Reservations.
Tip 5: Know the difference: Reserved Instances = billing discount with commitment; Capacity Reservations = guaranteed capacity with flexibility; On-Demand Capacity Reservations + Savings Plans = both benefits combined.
Tip 6: If a question presents a scenario where an organization needs to ensure instances can be launched during high-demand periods in a specific location, Capacity Reservations is typically the correct choice.