Attach service accounts to resources

For some Google Cloud resources, you can specify a user-managed service account that the resource uses as its default identity. This process is known as attaching the service account to the resource, or associating the service account with the resource.

When the resource needs to access other Google Cloud services and resources, it uses its attached service account as its identity. For example, if you attach a service account to a Compute Engine instance, and the applications on the instance use a client library to call Google Cloud APIs, those applications automatically authenticate as the attached service account.

This page describes how to configure service accounts so that you can attach them to resources.

Before you begin

Attach a service account to a resource

In most cases, you must attach a service account to a resource when you create that resource. After the resource is created, you cannot change which service account is attached to the resource. Compute Engine instances are an exception to this rule; you can change which service account is attached to an instance as needed.

Before you attach a service account to a resource, you must configure the service account. This process differs depending on whether the service account and the resource are in the same project or in different projects. After you configure the service account, you can create the resource and attach the service account to that resource.

Configure for a resource in the same project

Before you attach a service account to another resource in the same project, grant roles to the service account so it can access the appropriate resources, just as you would grant roles to any other principal.

Configure for a resource in a different project

In some cases, you might need to attach a service account to a resource that is located in a different project. For example, if you create all of your service accounts in a single project, you might need to attach one of them to a new resource in a different project.

Before you attach a service account to a resource in another project, do the following:

  1. In the project where the service account is located, follow the steps on this page to enable service accounts to be attached across projects.
  2. Identify the project where you will create the resource.

  3. Identify the type of resource that you will attach the service account to, as well as the service that owns that type of resource.

    For example, if you are creating a Pub/Sub subscription, then Pub/Sub is the service that owns the resource.

  4. Find the email address of the service agent for the service.

    Different services use different service agents. For details, see Service agents.

  5. Grant the Service Account Token Creator role (roles/iam.serviceAccountTokenCreator) to the service agents:

    Console

    1. In the Google Cloud console, go to the Service accounts page.

      Go to Service accounts

    2. Select the project that owns the service account that you will attach to a resource.

    3. Find the service account that you will attach to a resource, and select its checkbox.

    4. In the Permissions pane, click Add principal.

    5. In the New principals field, enter the email address of the service agent.

    6. In the Select a role drop-down list, type Service Account Token Creator, then click the role.

    7. Click Save to save your changes.

    8. Optional: If you need to grant the role to another service agent, repeat the previous steps.

    gcloud

    Use the gcloud iam service-accounts add-iam-policy-binding command:

    gcloud iam service-accounts add-iam-policy-binding \
    user-sa-name@project-id.iam.gserviceaccount.com \
    --member=serviceAccount:service-agent-email \
    --role=roles/iam.serviceAccountTokenCreator

    Replace the following values:

    • user-sa-name: The name of the user-managed service account that you are attaching to a resource.
    • project-id: The project ID where the user-managed service account is located.
    • service-agent-email: The email address for the service agent.

    The command prints the updated allow policy for the user-managed service account.

    Optional: If you need to grant the role to another service agent, run the command again.

    REST

    To grant this role, use the read-modify-write pattern to update the allow policy for your user-managed service account.

    First, read the allow policy for the user-managed service account:

    The projects.serviceAccounts.getIamPolicy method returns the allow policy for the service account.

    Before using any of the request data, make the following replacements:

    • PROJECT_ID: Your Google Cloud project ID. Project IDs are alphanumeric strings, like my-project.
    • USER_SA_NAME: The name of the user-managed service account that you are binding to a resource.

    HTTP method and URL: 

    POST https://iam.googleapis.com/v1/projects/PROJECT_ID/serviceAccounts/USER_SA_NAME@PROJECT_ID.iam.gserviceaccount.com:getIamPolicy

    Request JSON body: 

    {
  "requestedPolicyVersion": 3
}

    To send your request, expand one of these options:

    You should receive a JSON response similar to the following:

    {
  "version": 1,
  "etag": "BwWl3KCTUMY=",
  "bindings": [
    {
      "role": "roles/iam.serviceAccountUser",
      "members": [
        "serviceAccount:my-service-account@my-project.iam.gserviceaccount.com"
      ]
    }
  ]
}

    Next, modify the allow policy to grant the Service Account Token Creator role to the service agent. Replace SERVICE_AGENT_EMAIL with the email address for the service agent:

    {
  "version": 1,
  "etag": "BwWl3KCTUMY=",
  "bindings": [
    {
      "role": "roles/iam.serviceAccountTokenCreator",
      "members": [
        "serviceAccount:SERVICE_AGENT_EMAIL"
      ]
    },
    {
      "role": "roles/iam.serviceAccountUser",
      "members": [
        "serviceAccount:my-service-account@my-project.iam.gserviceaccount.com"
      ]
    }
  ]
}

    Finally, write the updated allow policy:

    The projects.serviceAccounts.setIamPolicy method updates the allow policy for your service account.

    Before using any of the request data, make the following replacements:

    • PROJECT_ID: Your Google Cloud project ID. Project IDs are alphanumeric strings, like my-project.
    • USER_SA_NAME: The name of the user-managed service account that you are binding to a resource.
    • SERVICE_AGENT_EMAIL: The email address of the service agent that will create access tokens for your user-managed service account.

    HTTP method and URL: 

    POST https://iam.googleapis.com/v1/projects/PROJECT_ID/serviceAccounts/USER_SA_NAME@PROJECT_ID.iam.gserviceaccount.com:setIamPolicy

    Request JSON body: 

    {
  "policy": {
    "version": 1,
    "etag": "BwWl3KCTUMY=",
    "bindings": [
      {
        "role": "roles/iam.serviceAccountTokenCreator",
        "members": [
          "serviceAccount:SERVICE_AGENT_EMAIL"
        ]
      },
      {
        "role": "roles/iam.serviceAccountUser",
        "members": [
          "serviceAccount:my-service-account@my-project.iam.gserviceaccount.com"
        ]
      }
    ]
  }
}

    To send your request, expand one of these options:

    You should receive a JSON response similar to the following:

    {
  "version": 1,
  "etag": "BwWo331TkHE=",
  "bindings": [
    {
      "role": "roles/iam.serviceAccountTokenCreator",
      "members": [
        "serviceAccount:SERVICE_AGENT_EMAIL"
      ]
    },
    {
      "role": "roles/iam.serviceAccountUser",
      "members": [
        "serviceAccount:my-service-account@my-project.iam.gserviceaccount.com"
      ]
    }
  ]
}

Attach the service account to the new resource

After you configure the user-managed service account, you can create a new resource and attach the service account to that resource. Make sure you create the new resource in the appropriate project.

See the instructions for the type of resource that you want to create:

Attaching a service account when creating a resource
AI Platform Prediction Model versions
AI Platform Training Jobs
App Engine standard environment App versions
App Engine flexible environment App versions
Cloud Composer Environments
Cloud Functions Cloud Function
Cloud Life Sciences Pipelines
Cloud Run Services
Cloud Scheduler Jobs
Cloud Source Repositories
Compute Engine
Dataflow Jobs
Datalab Instances
Dataproc Clusters
Google Kubernetes Engine
Notebooks Notebook instances
Pub/Sub Subscriptions
Vertex AI
Workflows Workflows

After you have created the resource and attached the service account to that resource, you can grant roles to the service account so it can access the appropriate resources. This process is the same as granting a role to any other principal.

To learn how to grant roles, see Granting, changing, and revoking access to resources.

Attach a service account to a resource in another project

By default, you cannot create a service account in one project and attach it to a resource in another project. If you want to keep all of your service accounts in one project, you must update the organization policy for that project.

Enable service accounts to be attached across projects

To let users attach service accounts in one project to resources in another project, check the following boolean constraints in the organization policy for the project where your service accounts are located:

  • Ensure that the iam.disableCrossProjectServiceAccountUsage boolean constraint is not enforced for the project.

    This boolean constraint controls whether you can attach a service account to a resource in another project. The constraint is enforced by default.

    When this constraint is not enforced, IAM adds a project lien that prevents the project from being deleted. This lien has the origin iam.googleapis.com/cross-project-service-accounts. We strongly discourage you from deleting this lien.

  • Recommended: Ensure that the iam.restrictCrossProjectServiceAccountLienRemoval boolean constraint is enforced for the project.

    This boolean constraint ensures that principals can remove the project lien only if they have the resourcemanager.projects.updateLiens permission at the organization level. If this constraint is not enforced, principals can remove the project lien if they have this permission at the project level.

To learn how to view or change a boolean constraint in an organization policy, see Setting a boolean constraint.

Disable service accounts from being attached across projects

If you previously enabled service accounts to be attached across projects, we strongly discourage you from disabling this feature, especially in production environments.

Specifically, in the project where your service accounts are located, you should not make any of these changes:

  • Do not update the project's organization policy to enforce the iam.disableCrossProjectServiceAccountUsage boolean constraint.
  • Do not update the project's organization policy to not enforce the iam.restrictCrossProjectServiceAccountLienRemoval boolean constraint.
  • Do not remove the project lien with the origin iam.googleapis.com/cross-project-service-accounts, which prevents you from deleting the project.
  • Do not delete the project.

If you are willing to accept the risk of disabling this feature, you can reduce your risk by disabling the service accounts that you are using across projects, then monitoring your Google Cloud environment for issues. If you see any issues, you can re-enable the service accounts. If you do not see any issues, then you might not have any Google Cloud resources that depend on a service account in a different project.

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