このエラーメッセージに関する原因と対処に関して説明します。
エラーメッセージ(英語)：
unable to connect to ec2
対処
関連リンク
AWS Developer Forums: Unable to connect to EC2 instance in VPC ...
https://forums.aws.amazon.com/thread.jspa?threadID=110906
Ansible AWS: Unable to connect to EC2 instance - Stack Overflow
https://stackoverflow.com/questions/45363067/ansible-aws-unable-to-connect-to-ec2-instance
Unable to connect to EC2 Instance : aws - Reddit
https://www.reddit.com/r/aws/comments/8zso95/unable_to_connect_to_ec2_instance/
amazon ec2 - Cannot connect to EC2 instance after converting ...
https://serverfault.com/questions/898313/cannot-connect-to-ec2-instance-after-converting-ubuntu-16-p・・・
amazon ec2 - aws cli tool set up - unable to connect ec2 and ...
https://serverfault.com/questions/632625/aws-cli-tool-set-up-unable-to-connect-ec2-and-retrieve-inst・・・
amazon ec2 - AWS inbound rules not working for security group ...
https://serverfault.com/questions/855817/aws-inbound-rules-not-working-for-security-group
How to ssh using putty to Amazon EC2 Linux Instance (AWS EC2 ...
https://www.youtube.com/watch?v=KRXaKDPlarc
https://www.youtube.com/watch?v=KRXaKDPlarc
Newest 'amazon-ec2' Questions - Page 3 - Super User
https://superuser.com/questions/tagged/amazon-ec2?page=3&sort=newest
amazon ec2 - Unable to connect to EC2 redmine - Super User
https://superuser.com/questions/1161661/unable-to-connect-to-ec2-redmine