How to reach new VMs (and IPs) in a VPC - AWS environment

[spiny]

Hi!

I created  a VPC in AWS and I have put pfsense as  main router/firewall, therefore if all the the VMs inside the VPC want to go out from the VPC they should pass through pfsense.

My question is: since I can create/shut down as much as VMs I want, How can pfsense knows that there are new VMs, new IP addresses and hence new routes? there is a protocol that allows pfSense router automatically to know if there are any changes in my VPC?

I was thinking about DHCP but it should not be working since AWS use its own DHCP. What do you think of DNS? It could be an option?