After assigning Elastic IP address, the EC2 instance is no longer accessible

Question

I create a new Amazon EC2 instance, and it is successfully working. I assign an Elastic IP address and after that my instance is not reachable. I did lots of changes in the VPC, ENI and Elastic IP address, but my instance is not reachable by public DNS, also in any region no EC2 instance is reachable by public DNS.

Answer 1

1. Check the security groups attached to the instance and whitelist your IP for required ports in security rules.

2. Check the NACL rules attached to the instance and see if there are any deny rules which is blocking your traffic.

3. Check whether your instance is passing 2/2 Status checks, Stop and Start or reboot your instance accordingly to resolve the status check failures.

4. Go to Instance actions --> Network Settings and get the instance screenshot, check whether you are able to see login screen or not.

5. Finally if you can get the instance logs from the Instance actions --> Network Settings and view logs to see if there are any issues while booting up the instance.

Since you are already confirmed that the instance is in public su.net and has DNS resolution enabled, one of the above step will definitely resolve your issue.

Answer 2

You need to assign an Inte.net gateway (IGW) to the su.net your EC2 instance belongs to so you can access over the Inte.net:

http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Inte.net_Gateway.html

Answer 3

sudo rm /root/.ssh/known_hosts

Enter this command to remove all the known hosts so ssh can make a fresh connection with the newly attached IP.

PS This will not affect any of your previous connections.