Instance connection is denied - CLIENT_FORBIDDEN [771]

It appears you're experiencing a complex issue with your Lightsail instance after reactivating your account. The CLIENT_FORBIDDEN [771] error typically indicates a problem with the instance's configuration or network settings, rather than an account-level block.

Here are some steps you can try to resolve the issue:

1. Check your instance's firewall settings in the Lightsail console. Ensure that port 22 (SSH) is open for inbound connections.

2. Verify that your instance is in a public subnet with an internet gateway attached, allowing for outbound traffic.

3. Review your instance's security group settings to confirm they allow the necessary inbound and outbound traffic.

4. Try rebooting the instance from the Lightsail console. If that doesn't work, try stopping and then starting the instance (note that this will change your public IP unless you're using a static IP).

5. Create a snapshot of your instance's root volume. This will allow you to recover your data and potentially attach it to a new, functioning instance if needed.

6. When creating a new instance from the snapshot, you can add a startup script to modify the SSH configuration. Add these lines to /etc/ssh/sshd_config:

   TrustedUserCAKeys /etc/ssh/lightsail_instance_ca.pub CASignatureAlgorithms +ssh-rsa

7. If possible, try to access the instance's serial console to troubleshoot any OS-level issues.

8. Consider upgrading to a larger Lightsail plan, as resource constraints could potentially cause connection issues.

If none of these steps resolve the problem, it may be necessary to contact AWS Support for further assistance. They can help identify any underlying issues with the instance or host system that aren't visible to you as a user.

Regarding the EC2 instance created from the Lightsail snapshot, the error suggests that EC2 Instance Connect is not properly configured. This is a separate issue from your Lightsail problem and would require additional configuration to resolve.

Remember, while AWS monitoring may show the instance as "working," this typically refers to the virtual machine being powered on and responding to basic health checks. It doesn't necessarily mean all services within the instance are functioning correctly.
Sources
EC2 Instance Connect cannot connect to my instance ! | AWS re:Post
Lightsail SSH - Connection (Request) Port 22: Connection timed out Issue . | AWS re:Post
CLIENT_UNAUTHORIZED [769] after update ubuntu | AWS re:Post

Hi,

Have you tried creating a root disk snapshot and attaching the disk to a newly created instance? https://docs.aws.amazon.com/lightsail/latest/userguide/amazon-lightsail-create-an-instance-root-volume-snapshot.html

1. You can create the snapshot with the CLI
2. Create a new instance with the console
3. Verify that you can connect to the new instance.
4. Create a disk from the snapshot.
5. Attach the disk to the newly created instance.

Hi,

There can be some delay to reinstate dependent services that Lightsail uses. Have you tried again recently? If its still not working, you can cut another support ticket to AWS.