You have a set of EC2 Instances hosting an nginx server and a web application that is used by a set of users in your organization. After a recent application version upgrade, the instance runs into technical issues and needs an immediate restart. This does not give you enough time to inspect the cause of the issue on the server. <strong> </strong>Which of the following options if implemented prior to the incident would have assisted in detecting the underlying cause of the issue?

Answer options:

A.Enable detailed monitoring and check the Cloudwatch metrics to see the cause of the issue.
B.Create a snapshot of the EBS volume after restart, attach it to another instance as a volume and then diagnose the issue.
C.Stream all the data to Amazon Kinesis and then analyze the data in real time.
D.Install Cloudwatch logs agent on the instance and send all the logs to Cloudwatch logs.

Answer – D
The AWS documentation mentions the following
You can publish log data from Amazon EC2 instances running Linux or Windows Server, and logged events from AWS CloudWatch. CloudWatch Logs can consume logs from resources in any region, but you can only view the log data in the CloudWatch console in the regions where CloudWatch Logs is supported. 
Option A is invalid as detailed monitoring will only help us to get more information about the performance metrics of the instances, volumes etc and will not be able to provide full information regarding technical issues.
Option B is incorrect if we had created a snapshot prior to the update it might be useful but not after the incident.
Option C is incorrect here we are dealing with an issue concerning the underlying application that handles the data so this solution will not help.
For more information on Cloudwatch logs, please refer to the below link:
http://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/StartTheCWLAgent.htm