I looked Amazon EKS webian and get recommendation for custom need use [amazon-eks-ami](https://github.com/awslabs/amazon-eks-ami) tools to embed own script into node group image.
Using this tool you can embed oneshot systemd unit that executed at server early boot process (`network.target`) and connect to server network interface with static private and public IP.
Later you use host network for Kamailio, rtpproxy, FreeSwitch daemons.
Think you can easily create bash or python network interface attachment script. Need just embed this script to API image.