You have a legacy application running that uses an m4.large instance size and cannot scale with Auto Scaling, but only has peak performance 5% of the time. This is a huge waste of resources and money. So your Senior Technical Manager has set you the task of trying to reduce costs while still keeping the legacy application, having lesser memory requirements, running in the long-term as it should. Which of the following will best accomplish the task your manager has assigned you? Choose the correct answer from the options below.

Answer options:

A.Use a "t2.medium - 3 yr RI" burstable performance instance.
B.Use a C4.large instance with enhanced networking.
C.Use two t2.nano instances that have single Root I/O Virtualization.
D.Use t2.nano instance and add spot instances when they are required.

Answer – A
The AWS documentation clearly indicates using T2 EC2 instance types for those instances that often don’t use CPU.
 T2
T2 instances are Burstable Performance Instances that provide a baseline level of CPU performance with the ability to burst above the baseline.
T2 Unlimited instances can sustain high CPU performance for as long as a workload needs it. For most general-purpose workloads, T2 Unlimited instances will provide ample performance without any additional charges. If the instance needs to run at higher CPU utilization for a prolonged period, it can also do so at a flat additional charge of 5 cents per vCPU-hour.
CPU Credits govern the baseline performance and ability to burst. T2 instances receive CPU Credits continuously at a set rate depending on the instance size, accumulating CPU Credits when they are idle, and consuming CPU credits when active. T2 instances are a good choice for various general-purpose workloads, including microservices, low-latency interactive applications, small and medium databases, virtual desktops, development, build and stage environments, code repositories, and product prototypes. For more information, see Burstable Performance Instances.
For more information on EC2 instance types, please see the below link:
https://aws.amazon.com/ec2/instance-types/
Option B is INCORRECT because using a "C4" instance would incur more costs and as per the requirements of the question, we need to reduce the costs. Please refer to the below link for instances pricing.
https://aws.amazon.com/ec2/pricing/on-demand/
Option C is INCORRECT because although "t2.nano" instance pricing is less, it has only 0.5 GiB of allocated memory, making the legacy application run too slow.
Option D is INCORRECT because there are chances that the spot instances would not be available when there is a need. Therefore, there are chances for the legacy application to break down for want of more instances when needed.