SSH keys are essential for securely connecting to Google Compute Engine virtual machine instances. They provide cryptographic authentication, allowing users to access Linux-based VMs through the Secure Shell protocol.
Google Cloud offers several methods for managing SSH keys:
1. **OS Login**: The…SSH keys are essential for securely connecting to Google Compute Engine virtual machine instances. They provide cryptographic authentication, allowing users to access Linux-based VMs through the Secure Shell protocol.
Google Cloud offers several methods for managing SSH keys:
1. **OS Login**: The recommended approach that uses IAM roles to manage SSH access. It links Linux user accounts to Google identities and provides centralized access management across your organization.
2. **Project-level metadata**: SSH public keys stored in project metadata are propagated to all VMs in that project. This method is suitable when you need consistent access across multiple instances.
3. **Instance-level metadata**: SSH keys can be added to individual VM instances, providing granular control over who can access specific machines.
4. **Temporary SSH keys**: When using the Cloud Console or gcloud command-line tool, Google can generate temporary SSH key pairs that expire after a short period.
To add SSH keys, you can use the gcloud CLI, Cloud Console, or the Compute Engine API. The format for metadata-based keys follows: USERNAME:SSH_PUBLIC_KEY.
Best practices include:
- Using OS Login for enterprise environments as it integrates with IAM and supports two-factor authentication
- Regularly rotating SSH keys to maintain security
- Removing keys for users who no longer require access
- Using instance-level keys when project-wide access is too permissive
- Blocking project-wide SSH keys on sensitive instances
When troubleshooting SSH connectivity issues, verify that firewall rules allow TCP port 22, the public key exists in metadata, and the private key matches the stored public key.
SSH keys work alongside other security measures like VPC firewall rules and IAM permissions to create a comprehensive security posture for your Compute Engine resources.
SSH Keys for Compute Engine - Complete Guide
Why SSH Keys for Compute Engine Matter
SSH keys are fundamental to secure access management in Google Cloud Platform. They provide a cryptographic method for authenticating to Compute Engine virtual machine instances, eliminating the need for passwords. Understanding SSH key management is essential for the GCP Associate Cloud Engineer exam because it directly impacts security, access control, and operational efficiency in cloud environments.
What Are SSH Keys in Compute Engine?
SSH keys are pairs of cryptographic keys consisting of a public key and a private key. The public key is stored on the VM instance, while the private key remains with the user. When a connection is attempted, the keys are used to verify identity through asymmetric encryption.
GCP supports several methods for managing SSH keys:
• Project-level SSH keys - Apply to all VMs in a project unless blocked • Instance-level SSH keys - Apply only to specific VM instances • OS Login - Links SSH access to IAM permissions and Google identities • Temporary SSH keys - Generated by Cloud Console or gcloud for one-time access
How SSH Key Management Works
Project-Level Keys: Keys added at the project level in Compute Engine metadata are propagated to all VM instances. Any user with a matching private key can access VMs where their public key is deployed. This approach is convenient but offers less granular control.
Instance-Level Keys: Keys can be added to individual instance metadata, providing more targeted access. You can also block project-level keys on specific instances by setting the block-project-ssh-keys metadata value to TRUE.
OS Login: This is the recommended approach for organizations requiring centralized access management. OS Login uses IAM roles to manage SSH access: • roles/compute.osLogin - Grants standard user access • roles/compute.osAdminLogin - Grants sudo/administrator access
To enable OS Login, set the metadata key enable-oslogin to TRUE at the project or instance level.
Connecting via gcloud: gcloud compute ssh INSTANCE_NAME --zone=ZONE
Enabling OS Login: gcloud compute project-info add-metadata --metadata enable-oslogin=TRUE
Security Best Practices
• Use OS Login for enterprise environments with many users • Block project-level SSH keys on sensitive instances • Regularly rotate and audit SSH keys • Use service accounts with appropriate scopes for automated access • Enable two-factor authentication with OS Login when possible
Exam Tips: Answering Questions on SSH Keys for Compute Engine
1. Know the hierarchy: Remember that instance-level metadata takes precedence over project-level metadata for SSH keys.
2. OS Login scenarios: When questions mention centralized identity management, IAM integration, or LDAP/Active Directory environments, OS Login is typically the correct answer.
3. Blocking project keys: If a question asks about restricting access to a specific VM while maintaining project-wide keys for others, look for answers involving block-project-ssh-keys metadata.
4. IAM roles for OS Login: Memorize the two key roles - compute.osLogin for regular access and compute.osAdminLogin for administrative privileges.
5. Metadata locations: Questions may test whether you understand that SSH keys are stored in instance or project metadata, not in IAM policies themselves.
6. Temporary access: When the Cloud Console or gcloud SSH commands are used, temporary keys are created and managed automatically by GCP.
7. Service accounts: For VM-to-VM communication or automated scripts, questions often involve service accounts rather than user SSH keys.
8. Troubleshooting scenarios: If a user cannot SSH to an instance, consider whether OS Login is enabled, whether the correct IAM roles are assigned, or whether project-level keys are blocked.