Google Compute Engine - can't ssh to it after debian upgrade - google-cloud-platform

Question

I upgraded my Debian instance from wheezy to jessie. Everything went well. I rebooted the system and couldn't ssh to it anymore from the compute engine instance page. I noticed the system did reboot, with a different external IP address. I'm able to get to a web server I have running on the virtual machine, so I know everything upgraded and rebooted properly. Google assigned a new external IP to it and I can't login anymore.

Answer 1

the fact that sshd is no longer running is very unlikely, so here is my personal debug steps when I can't reach an instance on Google Cloud:
Check twice you ssh parameters (ssh keys, login user, ip address)
Activate ssh debug logs (-v) when you try to connect
Try using Cloud Shell
Check firewall rules in GCP and on your local network
Check the boot logs on the instance serial port
Re-send you SSH key in GCP > Compute > Metadata (bugs occurs sometime with the google user agent on your machine)
After that, you normally know how to connect to your instance or you know what's wrong with sshd server.

Answer 2

You can review the serial-port logs of the affected instance for possible clue on the issue. If you have a snapshot of your instance disk, you can create a new VM. As per the issue, is possible that recent changes may have affected the instance boot sequence and the sshd_config file.
To troubleshoot this, you can enable interactive access, connect to the instance through the serial console and enter the serial port access information to access the disk, review the ssh config files$ sudo vi /etc/ssh/sshd_config and $ sudo vi /etc/ssh/ssh_config.
If you don’t have a root password for the serial console, you could use a startup script to add it to your instance as follows:
Go to the VM instances page in Google Cloud Platform console.
Click on the instance for which you want to add a startup script.
Click the Edit button at the top of the page.
Click on ‘Enable connecting to serial ports’
Under Custom metadata, click Add item.
Set 'Key' to 'startup-script' and set 'Value' to this script:
#! /bin/bash
useradd -G sudo USERNAME
echo 'USERNAME:PASSWORD' | chpasswd
Example:
#! /bin/bash
useradd -G sudo test1
echo 'test1:pass#100' | chpasswd
Click Save and then click RESET at the top of the page. You might need to wait for some time for the instance to reboot.
Click on 'Connect to serial port' on the page.
In the new window, you might need to wait a bit and press the Enter of your keyboard once; then, you should see the login prompt.
10.. Login using the USERNAME and PASSWORD you provided.
Example:
Username: test1 AND Password: pass#100
You can also share a sanitized version of the serial port logs, for more information on what may be happening on the instance. This is not due to a change in IP address, however the serial port logs should give us more insight.