I'm using AWS Outposts to run multiple Amazon Elastic Compute Cloud (Amazon EC2) instances. Why is the number of EC2 instances running on my Outpost less than the actual capacity?
The following Amazon CloudWatch metrics report the number of specific EC2 instance types available and used on your Outpost:
In some cases, the AvailableInstanceType_Count metric is zero. But, the number of EC2 instances running on your Outposts doesn't equal the actual capacity shown by the UsedInstanceType_Count metric.
This discrepancy happens when using AWS-managed services on your Outpost. Examples of AWS-managed services are Application Load Balancers or Amazon Relational Database Service (Amazon RDS). When used on Outposts, these types of services consume EC2 capacity but their associated instances aren't visible in your EC2 Dashboard. The UsedInstanceType_Count metric is the sum of your instances and any AWS-managed services instances running on your Outpost.
View the RDS Management console to confirm the number of RDS instances running on your Outpost.
Working with Amazon RDS on AWS Outposts
Subnets for your load balancer