Setting up OS Login

This document covers the basic steps for setting up OS Login.

OS Login lets you use Compute Engine IAM roles to grant or revoke SSH access to your Linux instances. OS Login is an alternative to managing instance access by adding and removing SSH keys in metadata. To learn more about the benefits of using this feature, see OS Login.

If you want to enable OS Login with a layer of security by using two-factor authentication, see Setting up OS Login with 2-step verification. To review all the options for managing access to your VMs, see Choosing an access method.

To configure OS Login and connect to your instances, complete the following steps:

  1. Install or update the guest environment.
  2. Optional: If you are an organization administrator, review Managing OS Login in an organization.
  3. Enable the OS Login feature on your project or on individual instances.
  4. Grant the necessary IAM roles to yourself or other principals.
  5. Connect to instances.

Before you begin

Limitations

  • OS Login is supported in private Google Kubernetes Engine (GKE) clusters running node pool versions 1.20.5 or later.

  • OS Login is not supported in public GKE clusters. Public cluster nodes continue to use metadata SSH keys when OS Login is enabled.

  • Currently, Fedora CoreOS images do not support OS Login. To manage instance access to VMs created using these images, use the Fedora CoreOS ignition system.

  • Windows Server and SQL Server images do not support OS Login.

Step 1: Install or update the guest environment

Your VM instance must have the latest version of the guest environment installed. Most public images already have the latest version installed. If you don't have the latest guest environment, update your guest environment.

If you have VMs that run custom images that you imported, install the guest environment on those VMs.

If you don't have the latest guest environment, update your guest environment.

Step 2: (Optional) Review managing OS Login in an organization

If you are organization admin, you can set some configurations such as enabling OS Login at the organization level. See Managing OS Login in an organization.

Step 3: Enabling or disabling OS Login

You can enable or disable OS Login by setting metadata values at the instance or project level. Enabling or disabling OS Login in instance metadata overrides the value that is set in project metadata. To set OS Login values, you can use either the Google Cloud Console or the gcloud command-line tool.

Console

You can apply the metadata values to your projects or VMs by using one of the following options:

  • Option 1: Set enable-oslogin in project-wide metadata so that it applies to all of the instances in your project.

    1. In the Google Cloud Console, go to the Metadata page.

      Go to Metadata

    2. Click Edit.

    3. Add a metadata entry, setting the key to enable-oslogin and the value to TRUE. Alternatively, set the value to FALSE to disable the feature.

    4. Click Save to apply the changes.

  • Option 2: Set enable-oslogin in the instance metadata of an existing instance.

    1. In the Google Cloud Console, go to the VM instances page.

      Go to VM instances

    2. Click the name of the instance that you want to enable OS Login on.

    3. On the instance details page, click Edit.

    4. Under Custom metadata, add a metadata entry, setting the key to enable-oslogin and the value to TRUE. Alternatively, set the value to FALSE to disable OS Login on the instance.

    5. Click Save to apply the changes to the instance.

  • Option 3: Set enable-oslogin in instance metadata when you create an instance.

    1. In the Google Cloud Console, go to the Create an instance page.

      Go to Create an instance

    2. Expand the Networking, disks, security, management, sole tenancy section, and then do the following:

      1. Expand the Management section.
      2. To add a metadata entry, in the Metadata section, click Add item. Then provide the following information:

        • Key: set the metadata key to enable-oslogin.
        • Value: set the metadata value to TRUE.

        Alternatively, set the value to FALSE to exclude the VM from the feature.

    3. Click Create.

gcloud

You can apply the metadata values on your projects or VMs using one of the following options:

  • Option 1: Set enable-oslogin in project-wide metadata so that it applies to all of the instances in your project.

    Use the project-info add-metadata command in the gcloud command-line tool and set a metadata value where oslogin=TRUE to enable OS Login:

    gcloud compute project-info add-metadata \
        --metadata enable-oslogin=TRUE
    

    Alternatively, you can set enable-oslogin to FALSE to disable OS Login.

  • Option 2: Set enable-oslogin in the metadata of an existing instance.

    Use the instances add-metadata command in the gcloud command-line tool and set oslogin=TRUE to enable OS Login. Replace VM_NAME with the name of your VM.

    gcloud compute instances add-metadata VM_NAME \
        --metadata enable-oslogin=TRUE
    

    Alternatively, you can set enable-oslogin to FALSE to exclude your instance from using OS Login.

  • Option 3: Set enable-oslogin in instance metadata when you create an instance.

    Use the instances create command in the gcloud command-line tool and set oslogin=TRUE to enable OS Login. Replace VM_NAME with the name of your instance.

    gcloud compute instances create VM_NAME \
        --metadata enable-oslogin=TRUE
    

    Alternatively, you can set enable-oslogin to FALSE to exclude your instance from using OS Login.

After you enable OS Login on the instances in your project, grant users permission to connect to those instances.

Step 4: Configuring OS Login roles on user accounts

Granting OS Login IAM roles

After you enable OS Login on one or more instances in your project, those VMs accept connections only from user accounts that have the necessary IAM roles in your project or organization.

To allow OS Login access to these VMs, you need to grant the necessary roles to the user. To allow OS Login access, complete the following steps:

  1. Grant one of the following instance access roles.

    You can grant these instance access roles at the instance level by using the gcloud compute instances add-iam-policy-binding command.

  2. If your VM uses a service account, then each user that connects to the VM using SSH has the ability to impersonate the service account. To ensure that the impersonation follows best practices, configure each user to have the roles/iam.serviceAccountUser role on the service account. To learn how to add access for a user to a service account, see Managing service account impersonation.

  3. For users that are outside of your organization to access your VMs, in addition to granting an instance access role, grant the roles/compute.osLoginExternalUser role. This role must be granted at the organization level by an organization administrator. For more information, see Granting instance access to users outside of your organization.

Granting SSH access to a service account

You can use OS Login roles to allow service accounts to establish SSH connections to your instances. This is useful for the following tasks:

You can grant SSH access to your service accounts by using the following process:

  1. Create a service account.
  2. Grant the necessary OS Login roles to your service account. Service accounts require the same roles as user accounts. To learn how to configure roles and permissions for service accounts, see Granting roles to service accounts.
  3. Provide Application Default Credentials to your service account, so that it can authorize requests to the necessary APIs. Provide Application Default Credentials using one of the following options:

After you grant SSH access to your service accounts, you can configure your apps to create SSH keys and establish SSH connections to other instances on your VPC networks. To see an example app for service account SSH, read the Connecting apps to instances using SSH tutorial.

Revoking OS Login IAM roles

To revoke user access to instances that are enabled to use OS Login, remove the user roles from that user account. For information about removing an IAM role for a user, see Granting, changing, and revoking access to resources.

When a user's access is revoked, the user will still have public SSH keys that are associated with their account, but those keys no longer function on the VM instances.

Step 5: Connect to instances

When you connect to a VM, you have three main options:

If you connect to a VM by using either the gcloud tool or SSH from the browser, Compute Engine automatically generates SSH keys and associates them with your user account. To connect to a VM using a third party tool, you first need to add the public keys to your user account.

After you connect to your instance, review the expected login behaviors.

Review expected login behaviors

  • On some instances using OS Login, you might receive the following error message after the connection is established:

    /usr/bin/id: cannot find name for group ID 123456789

    Ignore this error message. This error does not affect your instances.

  • Cloud Identity administrators can configure POSIX information and set a username for organization members. If a username is not set by a Cloud Identity administrator, OS Login generates a default Linux username by combining the username and domain from the email address associated with the user's Google profile. This naming convention ensures uniqueness. For example, if the user email associated with the Google profile is user@example.com, then their generated username is user_example_com.

    Optionally, Google Workspace organizations can change their default to remove the domain suffix for newly generated usernames. For example, if the user email address associated with the Google profile is user@example.com, then their generated username is user. For more information, see Managing the OS Login API.

    If a user is from a separate Google Workspace organization, the generated username is prefixed with 'ext_'. For example, if user@example.com is accessing a VM in a different organization, then their generated username is ext_user_example_com.

  • When you log in to an instance by using the gcloud compute ssh command, the login message has the following format for a user user that belongs to the example.com domain:

    Using OS Login user user_example_com instead of default user user

    This message confirms that the user is logging in with an OS Login profile.

What's next