We have a 3rd party integration which needs the EC2 instance IP to be whitelisted. The 3rd party whitelists the IP on their server and then only the EC2 instance can communicate with them.
In the case of single instance this works.
However when auto scaling kicks in, we would end up in more than 1 instance. These new instances automatically get new IPs for every autoscale action.
Is it possible for us to ask AWS to assign IPs from a say a set of 4 predefined Elastic IPs? ( Assumption is that autoscaling is restricted to say 4 and we have 4 floating EIPs )

I'm trying to avoid gateway NAT since there is a big cost associated with it.

Any ideas?