One of the easiest ways to monitor for underutilized or idle resources is to have AWS do it for you by using AWS Trusted Advisor. This service helps you optimize your AWS resources with AWS best practices by using built-in checks across categories like Security, Fault Tolerance, Performance, Service Limits, and Cost Optimization. 

Since we’re mainly talking about detecting underutilized resources, I’ll be mainly referring to the cost optimization checks in this video. These are designed to provide recommendations to reduce the cost of your AWS environment. I won’t go through every Trusted Advisor cost optimization check, but I will touch on some of the important ones. 

For example, with Trusted Advisor, you get built-in checks for idle resources, allowing you to easily find idle load balancers, RDS idle database instances, and unassociated IP addresses. It enables you to check for underutilized resources, such as low utilization EC2 instances, underutilized EBS volumes, underutilized Redshift clusters and Amazon comprehend underutilized endpoints. 

And it also enables you to check for over-provisioned resources, such as Amazon EBS over-provisioned volumes, AWS Lambda over-provisioned functions for memory size, AWS Lambda functions with excessive timeouts, and misconfigured resources like AWS Lambda functions with a high error rate. 

Note that these last four checks require you to opt-in to AWS Compute Optimizer before you get access to recommendations. Once these checks are performed, each check will be summarized into three main responses: 

1. Either it determines that an action is recommended, which shows as a red check
2. Or it detects that there may be an issue, and recommends Investigation, marking the check as yellow
3. Or it will signify that there are no problems detected and everything is good to go which will mark the check as green

With each check, you can view the recommended action and see AWS documentation that may help you better understand or fix the issue. 

For example, let’s say Trusted advisor runs the low utilization EC2 instances check. It then determines one of your instances only uses say 10% of its daily CPU utilization. In that case, it might recommend an action of stopping or terminating the instance, or using Auto Scaling to scale in instances when they’re not fully utilized. Note that it does not provide recommendations to modify or change the size of the instance - it only makes recommendations to delete. You can use AWS Compute Optimizer and AWS Cost Explorer Right Sizing recommendations to get modification recommendations instead. 

So who can use these AWS Trusted Advisor cost optimization checks? These checks are only available to those who pay for AWS Business Support, AWS Enterprise On-Ramp Support, or AWS Enterprise Support. 

If you use the basic or developer-level support plan, you do receive some checks on service limits and a few security checks - but you won’t have access to any of the other checks, including the cost optimization checks we talked about in this video. That being said, if you have at least the business support plan, using Trusted Advisor is one of the easiest ways to monitor for underutilized or idle resources.