A large finance company is utilizing OpsWorks for a website project. The website has been live for half a year. According to statistics, the average request volume varies throghout the day. The minimum average request volume requires five application server instances.

Answer options:

A.The stack should have five 24/7 instances, which are always on and handle the base load. Add ten schedule instances and modify the number of schedule instances every two hours, Add 2 spot instances to handle traffic spikes.
B.The stack should have five On Demand instances, which are used to serve the base load. Add ten schedule instances and modify the number of schedule instances every two hours. Add 2 spot instances to handle traffic spikes.
C.The stack should have five 24/7 instances to handle with base load. Add an EC2 autoscaling group to OpsWorks Stack and make sure that the launch configuration is proper. The autoscaling group is able to handle with the load change automatically. No other instances types are required.
D.The stack should have five 24/7 instances, which are always on and handle the base load. Add ten time-based instances and modify the number of time-based instances every hour. Add 2 load-based instances to handle traffic spikes.

CorrectAnswer – D
AWS OpsWorks Stacks provides three ways to manage the number of server instances.
24/7 instances are started manually and run until they are manually stopped.
Time-based instances are automatically started and stopped by AWS OpsWorks Stacks on a user-specified schedule.
Load-based instances are automatically started and stopped by AWS OpsWorks Stacks when they cross a threshold for a user-specified load metric such as CPU or memory utilization.
If you are managing stacks with more than a few application server instances, it is recommended to use a mix of all three instance types.
https://docs.aws.amazon.com/opsworks/latest/userguide/best-practices-autoscale.html
has discussed this scenario in details.
OptionA is incorrect: Because schedule instances and spot instances should not be used for OpsWorks stack.
Option B is incorrect: Because On demand/schedule/spot are EC2 instance types instead of OpsWorks instance types.
Option C is incorrect: Because it is improper to use EC2 autoscalling to maintain instance volume in OpsWorks. You can still configure that according to https://aws.amazon.com/blogs/devops/auto-scaling-aws-opsworks-instances/, however this is not a straightforward approach. The best practice suggested by AWS is using 24/7 instances/Time-based instances/Load-based instances to optimize the Number of Application Servers.