Why can't I ssh to an instance, given that SG and NACL are open?

What is the content for ~/.ssh/config? Is the instance located in public subnet with public ip?

Here I can see connection problem, not handshaking or authentication or something that comes later. As I can see you practically don't reach AWS. Is it possible your computer has some wrong DNS settings? what you get when you do

nslookup ec2-3-134-169-55.us-east-2.compute.amazonaws.com

IP definitely shouldn't be 0.0.0.1. Are you pointing to correct DNS server? maybe you have some old entries in /etc/hosts file?

This is becoming really intriguing. I got the same answer

W:\>ssh -v 1 -i  "/Users/user1/dev/intercloud/server-inter-cloud-us-east-2.pem" ec2-user@ec2-3-134-169-55.us-east-2.compute.amazonaws.com
Warning: Identity file /Users/user1/dev/intercloud/server-inter-cloud-us-east-2.pem not accessible: No such file or directory.
OpenSSH_for_Windows_7.7p1, LibreSSL 2.6.5
debug1: Connecting to 0.0.0.1 [0.0.0.1] port 22.
debug1: connect to address 0.0.0.1 port 22: Unknown error
ssh: connect to host 0.0.0.1 port 22: Unknown error

So you get the same issue (replacing values with your own, of course)?

The previous instances were created from the CLi. I created a new instance, with default settings, from the Console.

I got the same output in trying to connect to it.

Is the instance ... public ip?

Yes. The Console shows a public IP and DNS ec2-3-134-169-55.us-east-2.compute.amazonaws.com

Is the instance .. located in public subnet

Yes, the Routes shows (2) that traffic is routed to an Internet Gateway.

What is the content for ~/.ssh/config?

See (2) below. Nothing unusual from what I can see.

(1)

172.31.0.0/16	local
0.0.0.0/0	igw-8557c9ed

(2)

% cat ~/.ssh/config                                                                                                                                                                             
Host *
 ServerAliveInterval 30
 ServerAliveCountMax 5
 AddKeysToAgent yes
 IdentityFile ~/.ssh/id_ed25519


# Google Compute Engine Section
#
# The following has been auto-generated by "gcloud compute config-ssh"
# to make accessing your Google Compute Engine virtual machines easier.
#
# To remove this blob, run:
#
#   gcloud compute config-ssh --remove
#
# You can also manually remove this blob by deleting everything from
# here until the comment that contains the string "End of Google Compute
# Engine Section".
#
# You should not hand-edit this section, unless you are deleting it.
#
Host instance-1.us-west1-a.user1-proj
   HostName 34.105.77.134
   IdentityFile /Users/user1/.ssh/google_compute_engine
   UserKnownHostsFile=/Users/user1/.ssh/google_compute_known_hosts
   HostKeyAlias=compute.4640298531968040167
   IdentitiesOnly=yes
   CheckHostIP=no

# End of Google Compute Engine Section

what you get when you do... nslookup

See (1), which seems be be what we expect.

maybe you have some old entries in /etc/hosts file?

/etc/hosts is quite ordinary (see (2).

I went to a VM in Google Cloud, uploaded the pem file, and ran the same ssh command. I got the similar output with 0.0.0.1. However, this time the error message contains "invalid argument". See (3).

Also, EC2 Connect fails to connect.

some wrong DNS settings I have never changed my DNS settings and overall DNS works fine from this computer. The above tests seem to suggest that DNS is not the issue.

(1)

Server:		192.168.1.1
Address:	192.168.1.1#53

Non-authoritative answer:
Name:	ec2-3-134-169-55.us-east-2.compute.amazonaws.com
Address: 3.134.169.55

(2)

% cat /etc/hosts
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1	localhost
255.255.255.255	broadcasthost
::1             localhost
# Added by Docker Desktop
# To allow the same kube context to work on the host and the container:
127.0.0.1 kubernetes.docker.internal
# End of section

$  ssh -v 1 -i "/home/user1/server-inter-cloud-us-east-2.pem" ec2-userec2-3-134-169-55.us-east-2.comp
ute.amazonaws.com  
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1d  10 Sep 2019
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 0.0.0.1 [0.0.0.1] port 22.
debug1: connect to address 0.0.0.1 port 22: Invalid argument

So you also get that (changing the values to your own, of course)?

The earlier EC2 instances had been launched with the CLI,

So, I launched an EC instance from the Console. Same result, including the 0.0.0.1.

Good catch! Without the verbosity flag, we get a similar error (1). With maximum verbosity as you described, -vvv, we get a longer error message (2).

(1)

 % ssh -i "/Users/user1/dev/intercloud/server-inter-cloud-us-east-2.pem" ec2-user@ec2-3-134-169-55.us-east-2.compute.amazonaws.com
kex_exchange_identification: read: Connection reset by peer

(2)

% ssh -vvv -i "/Users/user1/dev/intercloud/server-inter-cloud-us-east-2.pem" ec2-user@ec2-3-134-169-55.us-east-2.compute.amazonaws.com
OpenSSH_8.1p1, LibreSSL 2.7.3
debug1: Reading configuration data /Users/user1/.ssh/config
debug1: /Users/user1/.ssh/config line 1: Applying options for *
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 47: Applying options for *
debug1: Connecting to ec2-3-134-169-55.us-east-2.compute.amazonaws.com port 22.
debug1: Connection established.
debug1: identity file /Users/user1/dev/intercloud/server-inter-cloud-us-east-2.pem type -1
debug1: identity file /Users/user1/dev/intercloud/server-inter-cloud-us-east-2.pem-cert type -1
debug1: identity file /Users/user1/.ssh/id_ed25519 type 3
debug1: identity file /Users/user1/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.1
kex_exchange_identification: read: Connection reset by peer