Which of the below mentioned CloudWatch metrics helps the user understand the issue with the instances?

A user has configured an ELB to distribute the traffic among multiple instances. The user
instances are facing some issues due to the back-end servers. Which of the below mentioned
CloudWatch metrics helps the user understand the issue with the instances?

A.
HTTPCode_Backend_3XX

B.
HTTPCode_Backend_4XX

C.
HTTPCode_Backend_2XX

D.
HTTPCode_Backend_5XX

Explanation:
CloudWatch is used to monitor AWS as well as the custom services. For ELB, CloudWatch
provides various metrics including error code by ELB as well as by back-end servers (instances.. It
gives data for the count of the number of HTTP response codes generated by the back-end
instances. This metric does not include any response codes generated by the load balancer.
These metrics are:
The 2XX class status codes represents successful actions
The 3XX class status code indicates that the user agent requires action
The 4XX class status code represents client errors
The 5XX class status code represents back-end server errors