Suddenly I can't connect to my ec2 server

Based on the information provided, there are several potential reasons why you might suddenly be unable to connect to your EC2 instance using EC2 Instance Connect. Here are some key areas to check:

1. Security Group Configuration: While you've shown that TCP port 22 is open in your inbound rules, it's important to ensure that the security group is correctly associated with your instance and that the rule is allowing access from the correct IP range for EC2 Instance Connect.

2. EC2 Instance Connect IP Ranges: AWS periodically updates the IP ranges used by EC2 Instance Connect. The security group needs to allow access from these IP ranges. You may need to update your security group to include the latest EC2 Instance Connect IP addresses for your region.

3. Instance State: Verify that your instance is still in the 'running' state. Sometimes instances can stop or terminate unexpectedly.

4. IAM Permissions: Ensure that your IAM user or role still has the necessary permissions to use EC2 Instance Connect. These permissions may have changed since your last successful connection.

5. EC2 Instance Connect Service: Check if the EC2 Instance Connect service is installed and running on your instance. It's possible that a system update or change may have affected this service.

6. Network Configuration: Confirm that your instance still has a public IP address and that there haven't been any changes to the VPC, subnet, or route table configurations that might affect connectivity.

To troubleshoot this issue:

1. Try to connect using SSH with your private key file to see if the problem is specific to EC2 Instance Connect.

2. Check the system logs in the EC2 console for any boot or connectivity issues.

3. Update your security group to allow access from the latest EC2 Instance Connect IP ranges. You can find these by querying the AWS IP range JSON file and filtering for EC2_INSTANCE_CONNECT in your region.

4. If possible, try connecting to the instance using AWS Systems Manager Session Manager as an alternative method to diagnose the issue.

If these steps don't resolve the issue, you may need to contact AWS Support for further assistance, especially if you suspect there might be an account-related problem.
Sources
Troubleshoot connection with EC2 Instance Connect | AWS re:Post
Connect to an Amazon EC2 instance using EC2 Instance Connect Endpoint - Amazon Elastic Compute Cloud
Can't connect to my EC2 instance | AWS re:Post
Can't connect to ec2 instance | AWS re:Post
Unable to connect to EC2 using EC2 instance connect | AWS re:Post

If you were able to connect to your EC2 instance previously but are now unable to do so, there could be several reasons for this issue.

1. Check Instance Status:

   • Go to the EC2 Dashboard in AWS Console.
   • Verify that your instance is running and not in a stopped or terminated state.

2. Check Security Group:

   • Ensure that the security group associated with your instance allows inbound SSH traffic (port 22) from your IP address.
   • Your IP address might have changed since your last connection.

3. Network ACLs:

   • If you're using custom Network ACLs, make sure they're not blocking SSH access.

4. Instance Health:

   • Check the system log and instance status checks in the EC2 console for any issues.

5. SSH Key:

   • Verify you're using the correct SSH key pair.
   • Ensure the permissions on your private key file are correct (chmod 400 your-key.pem).

6. DNS and IP Changes:

   • If you're using the public DNS name to connect, it might have changed if the instance was stopped and started.
   • Try using the public IP address instead.

7. VPN or Proxy:

   • If you're using a VPN or proxy, try connecting without it.

8. Firewall Settings:

   • Check if your local firewall is blocking outgoing SSH connections.

9. Instance Reachability Check:

   • In the EC2 console, select your instance and choose "Actions" > "Instance Settings" > "Get System Log" to see if there are any issues.

10. Network Issues:

    • There might be network issues on AWS's side. Check the AWS Service Health Dashboard for any reported issues.

11. SSH Client:

    • Try using a different SSH client or method (e.g., PuTTY instead of OpenSSH).

12. Restart the Instance:

    • As a last resort, try stopping and starting the instance (note: this will change its public IP if you're not using an Elastic IP).