Hi @Kannan,
You can check the official EC2 instances specification in AWS docs.
As you know, WebRTC is a high CPU consuming technology so it will be hard to try deploy OpenVidu with a t2 or t3 micro.
How many CPU’s cores do you need?
It all depends on your needs.
Check this OpenVidu Call: AWS c5.4xlarge >> 800-900 users possible?