One of the notable purchasing options that Amazon Web Services (AWS) offers to its clients is the Reserved Instance option. This model is an excellent way for AWS users to save money on their cloud usage, as the model offers up to 75% discounts on on-demand instance pricing. A user can commit to one or three years of usage for a specific instance type in exchange for these lower costs. However, as of today, Amazon has significantly improved its Reserved Instance option, bringing more flexibility to the customers.
Reserved Instance Flexibility
The primary benefit of reserved instances over on-demand instances was their lower cost. However, the lack of flexibility was a major drawback as users had to commit to a specific instance type for a long time. With the introduction of instance size flexibility, AWS has significantly improved the value proposition of reserved instances.
Instance Size Flexibility allows you to apply reserved instances across all sizes of instances within the same instance family and AWS region. This feature provides greater versatility because it does not lock you into a specific instance size.
For example, if you have a Reserved Instance for the m4.4xlarge instance, you can now use it for four m4.xlarge instances or eight m4.large instances.
Here’s a comparison table illustrating how Instance Size Flexibility works:
| Reserved Instance Purchased | Possible Usages |
|---|---|
| m4.4xlarge (16 vCPUs) | m4.4xlarge (16 vCPUs) |
| 2x m4.2xlarge (8 vCPUs each) | |
| 4x m4.xlarge (4 vCPUs each) | |
| 8x m4.large (2 vCPUs each) |
Regional Benefit for Reserved Instances
Apart from the Instance Size Flexibility, AWS also introduced another new feature known as “Regional Benefit for Reserved Instances.” In the traditional model, a Reserved Instance was tied to a specific Availability Zone. This meant that the benefit of the reserved instance was only applicable if the instance was spun up in that specific Availability Zone.
With Regional Benefit, a user can apply the Reserved Instance benefit across any Availability Zone in a specific region. This not only gives users geographic flexibility, but it also helps them to better manage their instances and respond to Availability Zone outages effectively.
For instance, if you are running instances in the US East (N. Virginia) region and you have purchased a Reserved Instance, the Reserved Instance benefit can be applied to an instance running in any of the available Availability Zones in the US East (N. Virginia) region.
In Conclusion
These two new features make Reserved Instances more attractive by providing both financial benefit and greater flexibility. Whether it is adapting to the unpredictability of your workloads, seamlessly scaling up your applications, or optimizing costs, AWS Reserved Instances with Instance Size Flexibility and Regional Benefit present a promising prospect for cloud users.
Keep in mind these are some of broader concepts regarding Reserved Instance flexibility that you need to understand for the AWS Certified Cloud Practitioner (CLF-C02) exam. However, the exam may confront you with more detailed questions or scenarios; hence, thorough understanding and consistent practice is recommended. Always refer back to AWS official documentation as the primary source of knowledge.
Keep learning, keep practicing, and good luck on your AWS Cloud Practitioner journey!
Practice Test
True or False: Reserved instances provide capacity reservations and significant savings on some AWS services.
- True
- False
Answer: True.
Explanation: Reserved instances allow customers to reserve capacity and can offer significant discounts compared to On-Demand Instance pricing.
Which of the following are features or benefits of Reserved Instances in AWS? (Choose all that apply)
- A. Cost savings
- B. Capacity reservations
- C. Billing visibility
- D. Short-term contracts
Answer: A, B, C
Explanation: Reserved instances provide cost savings, capacity reservations and billing visibility but they are generally for longer-term contracts (1-3 years), not short-term ones.
What types of Reserved Instances can be purchased in AWS? (choose all that apply)
- A. Standard Reserved Instances
- B. Convertible Reserved Instances
- C. Elastic Reserved Instances
- D. Scheduled Reserved Instances
Answer: A, B, D
Explanation: Convertible, Scheduled and Standard are types of Reserved Instances in AWS. Elastic Reserved Instances do not exist.
True or False: Reserved instances offer more flexibility than On-Demand instances.
- True
- False
Answer: False
Explanation: On-Demand instances provide more flexibility as they can be started/stopped at anytime, while Reserved Instances have to be purchased for a specific term (1 or 3 years).
Which of the following statements correctly describe Convertible Reserved Instances? (Choose all that apply)
- A. They allow changes in instance type during the term.
- B. They offer less savings than Standard Reserved Instances.
- C. They require a long-term commitment.
- D. They can be exchanged for different instances with higher values.
Answer: A, B, C, D
Explanation: Convertible Reserved Instances provide the flexibility to change instance types, but in turn, offer lesser savings than Standard Reserved Instances. These instances also require a long-term commitment and can be exchanged for different instances with higher values.
True or False: You cannot sell your unused Standard Reserved instances on the Reserved Instance marketplace.
- True
- False
Answer: False
Explanation: AWS offers an RI Marketplace where you can sell unused portions of your Standard Reserved Instances.
Can you modify the attributes of a Standard Reserved Instance in AWS?
- Yes
- No
Answer: No
Explanation: Unlike Convertible Reserved Instances, Standard Reserved Instances do not allow you to modify the instance attributes during the term.
How long are the terms for AWS Reserved Instances?
- A. 6 months
- B. 1 year
- C. 3 years
- D. 5 years
Answer: B, C
Explanation: AWS offers Reserved Instances terms for 1 year or 3 years, but not for 6 months or 5 years.
True or False: AWS Reserved Instances apply to databases, cache, and other services.
- True
- False
Answer: True
Explanation: While AWS Reserved Instances are commonly associated with EC2 instances, they can also apply to savings on other services.
To fulfill a Reserved Instance, AWS looks for instances that match which attributes? (Choose all that apply)
- A. Instance type
- B. Availability Zone
- C. Platform type
- D. Instance size flexibility
Answer: A, B, C, D
Explanation: AWS matches all the attributes including instance type, availability zone, platform type and instance size as long as instance size flexibility is enabled to fulfill a Reserved Instance.
Interview Questions
What is Reserved Instance flexibility in AWS?
Reserved Instance flexibility in AWS allows users to apply Reserved Instances (RI) across all sizes of instances within an instance family and across regions, letting you get the Reserved Instance pricing benefit across different sizes of instance.
Do Reserved Instances provide you with a capacity reservation for resources in AWS?
Yes, Reserved Instances also provide a capacity reservation which can give your confidence in your ability to launch the certain number of instances you have reserved when you need them.
How does having flexibility with Reserved Instances in AWS benefit users?
This flexibility allows AWS users to change their instance types to meet their business requirements without worrying about getting stuck in a long-term contract for an instance type that no longer serves their needs.
On what basis is the benefit from Reserved Instance flexibility applied?
The benefit is applied on a compute hour basis, i.e. regardless of the instance size, if you have purchased a RI for a given instance type, it will reduce costs for any instance within that family.
What is the feature called that allows you to apply Reserved Instances across regions?
A feature that allows you to apply Reserved Instances across regions is called Regional Benefit.
Can you exchange your AWS Reserved Instances once purchased?
Yes, AWS provides the flexibility to exchange reservations of a higher monetary value as your use cases evolve, permitting workload changes that may not align with the original reserved instances purchased.
Is Amazon EC2 Reserved Instance applicable to databases?
Yes, Amazon RDS, ElastiCache, and Redshift services also offer Reserved Instances.
Are Reserved Instances more cost-effective compared to On-Demand instances?
Reserved Instances can provide significant savings (up to 72%) compared to On-Demand instances.
What is meant by an “Instance Size Flexibility” in Reserved Instances?
Instance Size Flexibility is a feature of Amazon EC2 Reserved Instances that applies the discount of Reserved Instances to usage of any size in the instance family.
Can you sell your unused Reserved Instances in AWS?
Yes, AWS provides a Reserved Instance Marketplace for third-party sellers where they can sell their unused Reserved Instances.
Does cost depend on the usage of instance size flexibility?
Instance size flexibility does not change the cost of your Reserved Instances. You are billed at the same rate irrespective of instance size.
Can you share the benefit of Reserved Instances across AWS accounts?
Yes, organizations have the ability to share the cost benefits of Reserved Instances across their AWS accounts.
Is it possible to apply Reserved Instances to instances that are already running?
Yes, when you purchase a Reserved Instance, the billing benefit will be applied retroactively to any instances that have been running since the start of the hour.
Do all Amazon EC2 Reserved Instances offer instance size flexibility?
Not all Reserved Instances offer flexibility. For example, the Standard Reserved Instance for Linux and UNIX offers size flexibility within the same instance family and across AWS Regions, while Windows Reserved Instances do not.
What is the benefit term for Reserved Instances in AWS?
The Reserved Instances can be purchased with a one-year or three-year term commitment.
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