Getting two EC2 instances in the same security group to communicate

Question

I'm new to EC2 and I'm trying to setup an elasticsearch cluster. So far, I've been having trouble with discovery, so I want to get to the root problem by understanding how to telnet between two EC2 instances.

I have two t.micro instances setup
Both use the same security group called "elastic"

9300         sg-3bc28e0b (elastic)    
22 (SSH)     0.0.0.0/0
23 (TELNET)  0.0.0.0/0
9200         0.0.0.0/0

I installed telnet on both servers

When i try and telnet from one box to the other using the private IP, or public DNS I get "Connection refused"

When I'm on one EC2 instance, I've tried telnetting to the other by:

telnet 10.xxx.65.xxx 9300
telnet ec2-50-xxx-xx-127.us-west-2.compute.amazonaws.com 9300

Nothing works. What am i doing wrong? If I can't telnet from one box to the other, my understanding is that I'm not likely to have success with elasticsearch discover (which I haven't had with two other instances I setup and have since terminated).

Telnet port does not need to be open since you are not connecting on the telnet port. Make sure a service is running and listening on that port and that you have no software firewall installed on the instance that might be blocking connections. — datasage

icalvete icalvete · Accepted Answer · 2014-03-02T22:17:45

Open 9300 port for the security group where two instances are run (Even if same security group for both !!!)

Use Group ID value. For instance sg-18e1f37a

Getting two EC2 instances in the same security group to communicate

1 Answers