I recently setup a VPN server on AWS EC2(free tier), so I can log onto my gmail account in Mainland China. Here is a very clear and easy to follow step by step guide.

How to set up an ik2=ev2 vpn server with strongswan on ubuntu 18.04.02

Debug:

If you met some issue, please check ipsec log using below cmd:

systemctl status ipsec.service

Remember to also modify you security group on EC2, since it will only allow SSH protocal(tcp 22) as default