Can't SSH into an instance that was accessible only hours ago.

Question

I can't SSH into an EC2 t2 micro instance using Putty WinSCP or EC2 instant connect even though I haven't changed any of my credentials, the instant was accessible only an hour ago and the instance state is showing as running. When I try to access it I simply get 'Establishing connection' followed by 'Failed to connect to your instance Error establishing SSH connection to your instance. Try again later.' Uncertain how to go about figuring out what the problem is.

Answer

Hello.

Am I correct in assuming that you have not made any changes to the security group or network ACL settings?  
Can you also confirm that the global IP address you are using has not changed?  
The error message is generated when an attempt to connect using EC2 Instance Connect fails.  
A common cause of this error is misconfiguration of security groups or network ACLs.  
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-connect-set-up.html

It may also be possible to connect by setting the time on your terminal to the correct time as shown below.  
https://repost.aws/questions/QUXwRRF1F1Slu6Dx7sG8rBJg/ec2-error-establishing-ssh-connection-to-your-instance-please-wait-and-try-again-later#ANjOtzKw9BSV2WGS-_GjE1sA

Try stopping and starting EC2, as this may fix the problem.

Can't SSH into an instance that was accessible only hours ago.

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