About SSH connections

Linux Windows

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Compute Engine uses key-based SSH authentication to establish connections to all Linux virtual machine (VM) instances. You can optionally enable SSH for Windows VMs. By default, passwords aren't configured for local users on Linux VMs.

Before you can connect to a VM, several configurations must be performed. If you use the Google Cloud console or the Google Cloud CLI to connect to your VMs, Compute Engine performs these configurations on your behalf. Compute Engine performs different configurations depending on which tool you use to connect and whether you manage access to VMs through metadata or OS Login. OS Login is available only for Linux VMs.

Note: When a user connects to a VM, that user can use all of the IAM permissions granted to the service account attached to the VM.

Metadata-managed SSH connections

By default, Compute Engine uses custom project and/or instance metadata to configure SSH keys and to manage SSH access. All Windows VMs use metadata to manage SSH keys, while Linux VMs can use metadata keys or OS Login. If you use OS Login, metadata SSH keys are disabled.

Click each tab to learn more about the configurations Compute Engine performs before it grants SSH connections when you use the Google Cloud console, the gcloud CLI, or third party tools to connect to VMs. If you connect to VMs without using the Google Cloud console or the gcloud CLI, you must perform some configurations yourself.

Console

1. You use the SSH button in the Google Cloud console to connect to your VM.
2. Compute Engine sets a username and creates an ephemeral SSH key pair with the following configuration:
   • Your username is set as the username in your Google Account. For example, if the email address associated with your Google Account is [e-mail], then your username is cloudysanfrancisco.
     Note: You can override the default username by clicking the gear icon and selecting Change Linux Username when you connect to the VM.
   • Your public and private SSH keys are stored in your browser session.
   • Your SSH key has an expiry of five minutes. Five minutes after Compute Engine creates the key, you can't use the SSH key to connect to the VM anymore.
3. Compute Engine uploads the public SSH key and username to metadata.
4. Compute Engine retrieves the SSH key and username from metadata, creates a user account with the username, and on Linux VMs, stores the public key in your user's ~/.ssh/authorized_keys file on the VM. On Windows VMs, Compute Engine doesn't store the public key on the VM.
5. Compute Engine grants your connection.

gcloud

1. You use the gcloud compute ssh command to connect to your VM.
2. Compute Engine sets a username and creates a persistent SSH key pair with the following configurations:
   • Your username is set as the username in your local machine.
     
     Note: You can override the default username by providing a different username when you connect to the VM. Use the format USERNAME@VM_NAME.
   • Your public SSH key is stored in project metadata. If Compute Engine can't store the SSH key in project metadata, for example, because block-project-ssh-keys is set to TRUE, Compute Engine stores the SSH key in instance metadata.
   • Your private SSH key is stored on your local machine.
   • Your SSH key doesn't have an expiry. It is used for all future SSH connections you make, unless you configure a new key.
3. Compute Engine uploads the public SSH key and username to metadata.
4. Compute Engine retrieves the SSH key and username from metadata, creates a user account with the username, and on Linux VMs, stores the public key in your user's ~/.ssh/authorized_keys file on the VM. On Windows VMs, Compute Engine doesn't store the public key on the VM.
5. Compute Engine grants your connection.

Third party tools

1. You create an SSH key pair and username. See Create SSH keys for details.
2. You upload the public key and username to metadata. See Add SSH keys to VMs that use metadata-based SSH keys for details.
3. You connect to the VM.
4. Compute Engine retrieves the SSH key and username from metadata, creates a user account with the username, and on Linux VMs, stores the public key in your user's ~/.ssh/authorized_keys file on the VM. On Windows VMs, Compute Engine doesn't store the public key on the VM.
5. Compute Engine grants your connection.

Note: Google doesn't have access to your private key.

OS Login-managed SSH connections

Note: OS Login is only available for Linux VMs.

When you set OS Login metadata, Compute Engine deletes the VM's authorized_keys files and no longer accepts connections from SSH keys that are stored in project or instance metadata.

Click each tab to learn more about the configurations Compute Engine performs before it grants SSH connections when you use the Google Cloud console, the gcloud CLI, or third party tools to connect to VMs. If you connect to VMs without using the Google Cloud console or the gcloud CLI, you must perform some configurations yourself.

Console

1. You use the SSH button in the Google Cloud console to connect to your VM.
2. Compute Engine sets a username and creates an ephemeral SSH key pair with the following configuration:
   • Your username is the username set by your organization's Cloud Identity or Google Workspace administrator. If your organization hasn't configured a username for you, or your project doesn't belong to an organization, Compute Engine uses your Google Account email, in the following format:

     USERNAME_DOMAIN_SUFFIX

     For example, if the email associated with your Google Account is [e-mail], then your generated username is cloudysanfrancisco_gmail_com.

   • Your public SSH key is stored in your browser session and in your Google Account.
   • Your private SSH key is stored in your browser session.
   • Your SSH key has an expiry of three minutes. Three minutes after Compute Engine creates the key, you can't use the SSH key to connect to the VM anymore.
3. Compute Engine resolves your provided username to your OS Login account in the VM using NSS service modules.
4. Compute Engine performs IAM authorization using the AuthorizedKeysCommand, to ensure you have the required permissions to connect.
5. The AuthorizedKeysCommand retrieves the SSH key from your user account to provide it to OpenSSH in the VM.
6. Compute Engine grants your connection.

gcloud

1. You use the gcloud compute ssh command to connect to your VM.
2. Compute Engine sets a username and creates a persistent SSH key pair with the following configurations:
   • Your username is the username set by your organization's Cloud Identity or Google Workspace administrator. If your organization hasn't configured a username for you, Compute Engine uses your Google Account email, in the following format:

     USERNAME_DOMAIN_SUFFIX

     For example, if the email associated with your Google Account is [e-mail], then your generated username is cloudysanfrancisco_gmail_com.

   • Your public SSH key is stored in your Google Account.
   • Your private SSH key is stored on your local machine in the google_compute_engine file.
   • Your SSH key doesn't have an expiry. It is used for all future SSH connections you make, unless you configure a new key.
3. Compute Engine resolves your provided username to your OS Login account in the VM using NSS service modules.
4. Compute Engine performs IAM authorization using the AuthorizedKeysCommand, to ensure you have the required permissions to connect.
5. The AuthorizedKeysCommand retrieves the SSH key from your user account to provide it to OpenSSH in the VM.
6. Compute Engine grants your connection.

Third party tools

1. You create an SSH key pair. See Create SSH keys for details.
2. You upload your public SSH key to your OS Login profile. See Add keys to VMs that use OS Login for details.
• Compute Engine stores your key in your Google Account.
• Compute Engine configures your username in the default format:
  

      USERNAME_DOMAIN_SUFFIX

  For example, if the email associated with your Google Account is [e-mail], then your generated username is cloudysanfrancisco_gmail_com.
3. You optionally set a username with the Google Workspace Admin SDK Directory API.
4. You connect to the VM.
5. Compute Engine resolves your provided username to your OS Login account in the VM using NSS service modules.
6. Compute Engine performs IAM authorization using the AuthorizedKeysCommand, to ensure you have the required permissions to connect.
7. The AuthorizedKeysCommand retrieves the SSH key from your user account to provide it to OpenSSH in the VM.
8. Compute Engine grants your connection.

Note: Google doesn't have access to your private key.

What's next?

• Learn more about the benefits of using OS Login.
• Set up OS Login to manage access to your VMs.
• Learn how to Manage SSH keys in metadata, if you don't want to use OS Login.
• Learn how to Connect to VMs.
• To find methods and tools for diagnosing and resolving failed SSH connections, see Troubleshooting SSH.