There is a major flaw in placement of the EC2 instance in this diagram.
Each EC2 instance has 1 or more Network Interfaces, where each Network Interface resides in 1 subnet and can have multiple public and private IP addresses. The diagram currently suggests that an EC2 instance is located in a single subnet — it’s not. Each Network Interface connected to an EC2 instance is only required to be in the same Availability Zone where the instance was launched.
Each EC2 instance has 1 or more Network Interfaces, where each Network Interface resides in 1 subnet and can have multiple public and private IP addresses. The diagram currently suggests that an EC2 instance is located in a single subnet — it’s not. Each Network Interface connected to an EC2 instance is only required to be in the same Availability Zone where the instance was launched.