You have an Opswork stack defined with Linux instances. You have executed a recipe , but the execution has failed. Which of the following options would you use to diagnose the reason of the failure?

Answer options:

A.Use AWS Cloudtrail and check the Opswork logs to diagnose the error
B.Use AWS Config and check the Opswork logs to diagnose the error
C.Log into the instance and check if the recipe was properly configured.
D.Deregister the instance and check the EC2 Logs

Answer - C
The AWS Documentation mentions the following
If a recipe fails, the instance will end up in the setup_failed state instead of online. Even though the instance is not online as far as AWS OpsWorks Stacks is concerned, the EC2 instance is running and it`s often useful to log in to troubleshoot the issue. For example, you can check whether an application or custom cookbook is correctly installed. The AWS OpsWorks Stacks built-in support for SSH and RDP login is available only for instances in the online state. 
For more information on Opswork troubleshooting, please visit the below URL:
http://docs.aws.amazon.com/opsworks/latest/userguide/troubleshoot-debug-login.html