google-compute-engine – Unable to Open JupyterLab on Google Compute Notebook Instance

It looks like you've added AllowUsers in /etc/ssh/sshd_config configuration file.

To resolve this issue, you'll need to attach the boot disk of your VM instance to a healthy instance as the second disk. Mount it, edit the configuration file and fix the issue.

Here are the steps you can take to resolve the issue:

1. First of all, take a snapshot of your instance’s disk, in case if a loss or corruption happens you can recover your disk.

2. In the Developers Console, click on your instance. Uncheck Delete boot disk when instance is deleted and then delete the instance. The boot disk will remain under “Disks”, and now you can attach the disk to another instance. You can also do this step using gcloud command:

   $ gcloud compute instances delete NAME --keep-disks all
   

3. Now attach the disk to a healthy instance as an additional disk. You can do this through the Developers Console or using the gcloud command:

   $ gcloud compute instances attach-disk EXAMPLE-INSTANCE --disk DISK --zone ZONE
   

4. SSH into your healthy instance.

5. Determine where the secondary disk lives:

   $ ls -l /dev/disk/by-id/google-*
   

6. Mount the disk:

   $ sudo mkdir /mnt/tmp
   $ sudo mount /dev/disk/by-id/google-persistent-disk-1-part1 /mnt/tmp
   

Where google-persistent-disk-1 is the name of the disk

7. Edit sshd_config configuration file and remove AllowUsers line and save it.

   $ sudo nano /mnt/tmp/etc/ssh/sshd_config
   

8. Now unmout the disk:

   $ sudo umount /mnt/tmp
   

9. Detach it from the VM instance. This can be done through the Developers Console or using the command below:

   $ gcloud compute instances detach-disk EXAMPLE-INSTANCE --disk DISK
   

10. Now create a new instance using your fixed boot disk.

That is a strange behavior. If a VM is recreated in the same network, Google Firewall rules will still apply. In general there are a couple of things you might want to look at:

1) Check that the Google Firewall rule is still valid. For example if you recreate the VMs without metadata tags and the firewall rule was using them, traffic will get blocked.

2) Confirm that the VM itself is not running a firewall that is dropping the packets.

3) Check that the VM has a service listening on the appropriate port netstat --listen

4) As already mentioned, check the routes on Google project.

The use of tools like nmap or telnet can also help to troubleshoot.