AWS console indicates instance is all OK, but cannot connect

Hello,

There are a number of possibilities that can cause SSH time out issues but I will try to narrow down to the most likely cause based on your information provided.

It sounds like this instance was accessible at some point before the outage you are referring to so unless security groups, network access control lists, and ENIs have not been reconfigured, most AWS-level traffic issues should be ruled out. What is likely happening is that if there was an outage and your instance was restarted, a local OS-level firewall might have been refreshed and could now be blocking your connections. I would recommend checking reference number 3 below for a method to get around this using user-data if this is indeed the case.

Given all system and instance status checks are not failing, sometimes looking at your instance resources via CloudWatch can give you an idea if CPU, networking, or EBS utilization might be playing a part in the issue as well in the sense that they could be over-utilized and not providing enough resources to complete the SSH request. I would recommend checking all of these metrics against your instance and EBS volume's limits.

[1] SSH Troubleshooting - https://aws.amazon.com/premiumsupport/knowledge-center/ec2-linux-ssh-troubleshooting/

[2] Troubleshoot EC2 Timeout - https://aws.amazon.com/premiumsupport/knowledge-center/instance-vpc-troubleshoot/

[3] Resolve "Connection Refused" or "Connection Timed Out" Errors - https://aws.amazon.com/premiumsupport/knowledge-center/ec2-linux-resolve-ssh-connection-errors/