How to assign Elastic IP address from a selected list of Elastic Ip addresses to an Auto scaling group

Assuming your auto scaling group instances are in a private subnet. The private subnet has a route in its route table that routes all internet traffic (0.0.0.0/0) to the NAT Gateway. The NAT Gateway is in a public subnet that has a route table with a route that sends all internet traffic to the Internet Gateway. The NAT Gateway has an Elastic IP. This is the IP address that you provide to the external service. All the traffic from the auto scaling group instances will look like the requests are coming from the NAT Gateway Elastic IP address from the external service point of view.

If you have a multi-AZ architecture for your auto scaling group, you will need a NAT Gateway in each AZ with the private subnet route table pointing to this NAT Gateway. NAT Gateways are highly available within an AZ. You will then need to supply your external service with the Elastic IP assigned to this second NAT Gateway.

Thanks for quick answer. I really appreciate.