SSH Connection Issue with Ubuntu EC2 Instance

Based on the information you've provided, it seems you've covered several of the common causes for SSH connection issues. However, there are a few additional things you can check to troubleshoot this problem:

1. EC2 Instance Connect compatibility: Ensure that your Ubuntu instance is compatible with EC2 Instance Connect. Some Ubuntu AMIs may require additional configuration to work with this feature.

2. Security group configuration: While you've allowed inbound traffic on port 22 from your IP address, for EC2 Instance Connect to work properly, you also need to allow inbound SSH traffic from the EC2 Instance Connect service IP range for your region. You can find these IP ranges by running a specific AWS CLI command for your region.

3. IAM permissions: Verify that you have the necessary IAM permissions to use EC2 Instance Connect. You may need to create and attach an IAM policy that allows pushing a public key to the instance metadata.

4. Instance metadata: Ensure that the EC2 Instance Connect package is installed and properly configured on your Ubuntu instance.

5. Network connectivity: Check that your instance is in a subnet with a route to an Internet Gateway if you're trying to connect from the internet. Also, verify your Network Access Control Lists (NACLs) are allowing the necessary inbound and outbound traffic.

6. Time synchronization: Ensure that the time on your local machine is correctly synchronized with the AWS region time where your instance is located. Time discrepancies can sometimes cause connection issues.

7. SSH client configuration: If you're using the EC2 Instance Connect CLI, make sure your security group allows access from your local IP address as well.

If you've checked all these points and are still experiencing issues, you may want to try connecting using a standard SSH client with verbose output to get more detailed error messages. This can provide additional insights into what might be causing the connection failure.

If the problem persists, you might consider using the EC2 Serial Console or AWS Systems Manager Session Manager as alternative methods to access your instance and further investigate the issue.
Sources
Troubleshoot connection with EC2 Instance Connect | AWS re:Post
EC2: Error establishing SSH connection to your instance. Please wait and try again later. | AWS re:Post
Tutorial: Complete the configuration required to connect to your instance using EC2 Instance Connect - Amazon Elastic Compute Cloud
Troubleshoot issues connecting to your Amazon EC2 Linux instance - Amazon Elastic Compute Cloud

To connect to an AWS Ubuntu instance via SSH, you need to follow these steps:

1. Launch an EC2 instance: First, you need to have an Ubuntu EC2 instance running in your AWS account. Make sure you have the private key (.pem file) associated with this instance.

2. Ensure proper security group settings: Your instance's security group should allow inbound SSH traffic (port 22) from your IP address or a range of IP addresses you'll be connecting from.

3. Obtain the public IP or public DNS of your instance: You can find this information in the EC2 console under the "Description" tab of your instance.

4. Connect using SSH client:

For Linux or macOS users:

a. Open a terminal b. Change the permissions of your private key file:

chmod 400 /path/to/your-key.pem

c. Use the ssh command to connect:

ssh -i /path/to/your-key.pem ubuntu@your-instance-public-dns

For Windows users:

a. Use an SSH client like PuTTY

b. Convert the .pem file to .ppk format using PuTTYgen

c. In PuTTY, set the host name as ubuntu@your-instance-public-dns

d. In the SSH > Auth section, browse and select your .ppk file

e. Click "Open" to start the SSH session

By following these steps and referring to the official AWS documentation, you should be able to successfully connect to your AWS Ubuntu instance via SSH.

[+] https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/connect-linux-inst-ssh.html

Did you try connecting from a different computer? This seems like an issue with your computer rather than the EC2 instance as the steps you have taken seem to be correct.