I have launched two AWS RHEL7 instances in US East and West regions . I'm not able to ssh to instance2 from instance1 [using private ip]
In the security groups , I have added SSH rule for both the instances.
ssh: connect to host 172.X.X.X port 22: No route to host
I'm using Putty to connect to those instances as my local OS is Windows .
If your two instances are in different regions, they will not be able to connect to each other by default. They are isolated. AWS does not provide any way for you to directly link two networks in two different regions using private IPs.