Lost Connection: Why You Can't SSH into Your Google Cloud VM After a Restart
The Problem: You've just restarted your Google Cloud Virtual Machine (VM), and now you can't connect to it using your SSH client through the browser. You're stuck, staring at a timeout error, and your project is on hold.
Simplified: Imagine you're trying to open your front door, but the key doesn't work anymore. You're locked out of your VM, even though it's running.
Scenario:
Let's say you're using Google Cloud Console and have set up an SSH connection to your VM. You've been working away, but then you decide to restart the VM for maintenance or to apply updates. After the restart, when you try to SSH back in, you're greeted with a dreaded "Connection timed out" error.
Original Code (Example):
gcloud compute ssh my-vm --zone us-central1-a
The Culprit: Firewall Rules and IP Address Changes
The most common culprit is a change in the VM's IP address after the restart. When you restart your VM, Google Cloud sometimes assigns it a new internal IP address. This change can disrupt your SSH connection because the firewall rules might not be updated to allow access to the new IP.
Here's why this happens:
- Dynamic IP Allocation: Google Cloud uses dynamic IP allocation for VMs, meaning the IP address is not static and can change during restart.
- Firewall Rules: Your firewall rules are configured to allow SSH access to a specific IP address (either your external IP or a specific range). When the VM restarts, the IP changes, making the firewall rule ineffective.
Troubleshooting Steps:
- Check Firewall Rules:
- Go to the Google Cloud Console and navigate to "Virtual Private Networks" -> "Firewall."
- Check if your firewall rules are configured correctly. Ensure they allow SSH traffic on port 22 to the new IP address of your VM.
- If the rules are outdated, update them to allow access to the current IP address.
- Get the New IP Address:
- In the Google Cloud Console, go to "Compute Engine" -> "VM Instances."
- Look for your VM instance and check its internal IP address.
- If the IP address has changed, you need to update your firewall rules accordingly.
- Re-establish the Connection:
- Once you have verified and updated your firewall rules, try re-establishing your SSH connection using the new IP address.
Additional Insights:
- Static IP Addresses: If you need a stable IP address, consider using a static IP address for your VM. This can be done through the Google Cloud Console.
- SSH Tunneling: If you are experiencing persistent connection issues, try setting up an SSH tunnel to access your VM. This can bypass firewall problems and provide a more stable connection.
Conclusion:
Losing SSH access to your VM after restarting it can be frustrating. By understanding the cause behind the issue, you can quickly troubleshoot and regain access to your VM. Remember to verify your firewall rules and ensure they are configured to allow access to the current IP address of your VM.
