A Web-application uses Amazon SQS to buffer messages processed by another application deployed in a fleet of Amazon EC2 instances. Application deployed on Amazon EC2 instances sends message confirmation to end-users. Due to the heavy load on Amazon EC2 instances, it takes a long time to process messages & users are receiving multiple messages. Which of the following changes can be done on the Amazon SQS queue to ensure users receive only a single message?

Answer options:

A.Increase visibility timeout to 5 mins using ChangeMessageVisibility.
B.Increase visibility timeout to 5 mins using UpdateMessageVisibility.
C.Decrease visibility timeout to 2 mins using UpdateMessageVisibility.
D.Decrease visibility timeout to 2 mins using ChangeMessageVisibility.

Correct Answer – A
Visibility Timeout is used to hide messages from other consumers when one of the consumers is processing the message. In the above case, when one of the Amazon EC2 instances is processing messages from the Amazon SQS queue, it takes time to process messages due to load on the instance. Within that time period, visibility timeout is expired & another EC2 instance is processing the same message & sending updates to users. To avoid multiple processing of the same message, the Visibility timeout can be increased so that Amazon EC2 processes the message before the visibility timeout expires. 
Option B & D are incorrect as UpdateMessageVisibility is an invalid option to change the visibility timeout.
Option C is incorrect as decreasing visibility timeout will not resolve the issue.
For more information on visibility timeout with Amazon SQS, refer to the following URL-
https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-visibility-timeout.html