AWS EC2 instance unable to ssh remote server

Asked Jan 04 '19 at 22:37

Active Jan 06 '19 at 04:14

Viewed 115 times

I have 2 EC2 Ubuntu instances: Instance-A and Instance-B. Both's ufw shows inactive and they are in the same subnet of a VPC. Both's security group allows all inbound and outbound traffic from anywhere. And they have identical ssh_config.

From command line of Instance-B, I can ssh to any of my SSH servers, either they are in the same VPC or non-AWS server.

However, from commaind line of Instance-A, I can only ssh to Instance-A and Instance-B using their private IP. I cannot ssh either (even Instance-A itself) using their public IP. Neither can I log in to any non-AWS server. The error is 'connection timeout'.

How can I make Instance-A' ssh client work?

[added facts]

In Instance-A, I can ping google.com, A's public IP, B's public IP
ssh client used to work well in Instance-A. I don't know what has changed.

edited Jan 06 '19 at 04:14

asked Jan 04 '19 at 22:37

Dustin Sun

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Are they in a public subnet? Do both instances have a Private IP? – John Rotenstein Jan 05 '19 at 07:48
@JohnRotenstein yes they are both in public subnet and both have their own private IP – Dustin Sun Jan 06 '19 at 03:43
Maybe add or modify the security group associated with the ec2 instance so it can allow for external traffic on the appropriate port #. Make sure both ec2 instances have are in the same security group and make sure it allows for traffic – smitty_werbenjagermanjensen Jan 06 '19 at 04:20
@JoeA security group was the first thing I checked and I think it is fine. Moreover, to completely isolate the cause of the issue I have changed both inbound and outbound rules to allow any connection from any IP – Dustin Sun Jan 06 '19 at 04:24
Oops, I meant do they both have a Public IP (not Private). – John Rotenstein Jan 06 '19 at 08:38
@JohnRotenstein yes they do – Dustin Sun Jan 06 '19 at 16:04
Maybe this answer: https://stackoverflow.com/questions/26706683/ec2-t2-micro-instance-has-no-public-dns – smitty_werbenjagermanjensen Jan 07 '19 at 18:49
@JoeA My question is different as Instance-B does have a public IP and I can ssh to it from local PC. Besides, I can ping google.com and Instance-A's public IP. Anyway, Instance-B has been terminated and I will likely never find the answer. – Dustin Sun Jan 07 '19 at 20:02
Oh I'm sorry I misunderstood. I apologize for not being able to help you. – smitty_werbenjagermanjensen Jan 07 '19 at 20:19
@JoeA Please don't be. Your comments and questions were highly appreciated! – Dustin Sun Jan 07 '19 at 20:38
@lonelyloner thank you for the kind words I appreciate it – smitty_werbenjagermanjensen Jan 07 '19 at 20:55

AWS EC2 instance unable to ssh remote server

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