Windows EC2 instances in same security group cannot communicate

Question

I have 2 instances (windows machine) in the same security group.

I create a network drive on instance machine(A) for share a folder to other instance machine(B). But when I map a network path on machine(B), windows cannot find the path.

Here are my Security group setting:

ALL TCP Port 0-65535, Source 0.0.0.0/0    
ALL UDP Port 0-65535, Source 0.0.0.0/0    
RDP Port 3389 , Source 0.0.0.0/0

I tried turn off firewall, but still cannot link 2 computer together.

I am 0 knowledge on networking, so I don't know how to use other method to check my instance machine are connected together or not.

Answer 1

Allow access to instances in your existing security group to itself. Here's a screenshot of the EC2 management console. Let say you servers were in a group called "mygroup". Create a custom rule for "mygroup" and allowing the source "mygroup" access on all ports: