How to Duplicate an EC2 Instance for HA Purpose

Is there a way to duplicate a EC2 instance in the same VPC in different AZ for HA purpose, so that when the primary instance is bad (e.g. due to check status failure), I can shut it down and quickly switch over to the standby one.

For some reason, I need to keep the same private IP address, and public/EIP IP address. For the EIP address, I can dis-associate it from the OLD instance, and re-associate it to the NEW instance, but how about the private IP address?

Any suggestion? Thanks in advance...