What action should you take if EC2 instances are polling empty SQS queues and burning CPU cycles?

Enabling SQS long polling is the most effective action to take in this scenario because it reduces the number of empty responses to your EC2 instances that are retrieving messages from the SQS queue. With short polling, EC2 instances may frequently query the SQS queue, leading to instances receiving an empty response, which can result in unnecessary CPU usage and costs. Long polling allows the SQS service to hold the request open for a configurable duration, up to 20 seconds, waiting for a message to arrive. This means that if there are no messages, the instance will wait and not immediately receive an empty response, thus minimizing the CPU cycles consumed by continually polling an empty queue.

Increasing CPU resources would not address the fundamental issue of instances polling for messages that are not there; it would merely increase capacity where it's not needed. Decreasing the number of EC2 instances might reduce costs but could also lead to delays in processing messages once they do arrive in the queue. Opting for a different messaging service may not be necessary when an existing feature like long polling can efficiently resolve the issue.