Attach service accounts to resources  |  IAM Documentation  |  Google Cloud (2024)

For some Google Cloud resources, you can specify a user-managed service account that theresource uses as its default identity. This process is known as attaching the serviceaccount to the resource, or associating the service account with the resource.When code running on the resource accesses Google Cloud services and resources, it uses theservice account attached to the resource as its identity. For example, if you attach aservice account to a Compute Engine instance, and the applications on the instance use a client library to call Google Cloud APIs,those applications automatically use the attached service account for authentication andauthorization.

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

Before you begin

• Enable the IAM and Resource Manager APIs.

  Enable the APIs

• Make sure you understand how service accounts work inIAM.

Required roles

To get the permission that you need to attach a service account to a resource, ask your administrator to grant you the Service Account User (roles/iam.serviceAccountUser) IAM role on the service account. For more information about granting roles, see Manage access to projects, folders, and organizations.

This predefined role contains the iam.serviceAccounts.actAs permission, which is required to attach a service account to a resource.

You might also be able to get this permission with custom roles or other predefined roles.

Attach a service account to a resource

In most cases, you must attach a service account to a resource when you createthat resource. After the resource is created, you cannot change which serviceaccount is attached to the resource. Compute Engine instances are anexception to this rule; you canchange which service account is attached to an instanceas needed.

Before you attach a service account to a resource, you must configure theservice account. This process differs depending on whether the service accountand the resource are in the same project or in different projects. After youconfigure the service account, you can create the resource and attach theservice 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 canaccess the appropriate resources, just as you would grant roles to any otherprincipal.

Configure for a resource in a different project

In some cases, you might need to attach a service account to a resource that islocated in a different project. For example, if youcreate all of your service accounts in a single project, youmight 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 thefollowing:

1. In the project where the service account is located, follow the steps onthis page toenable 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, thenPub/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, seeService 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 aresource.

   3. Click the email address of the service account that you will attach to aresource.

   4. Go to the Permissions tab and find the section Principals with accessto this service account.

   5. Click person_addGrant access, and then enter the email address of the service agent.

   6. Click Select a role, type Service Account Token Creator, and clickthe role.

   7. Click Save to save your changes.

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

   gcloud

   Use thegcloud iam service-accounts add-iam-policy-bindingcommand:

   gcloud iam service-accounts add-iam-policy-binding \ SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com \ --member=serviceAccount:SERVICE_AGENT_EMAIL \ --role=roles/iam.serviceAccountTokenCreator

   Replace the following values:

   • SERVICE_ACCOUNT_NAME: The name of the user-managedservice account that you are attaching to a resource.
   • PROJECT_ID: The project ID where the user-managedservice account is located.
   • SERVICE_AGENT_EMAIL: The email address for the serviceagent.

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

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

   REST

   To grant this role, use the read-modify-write pattern to update the allow policyfor 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 projectID. 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:

   curl (Linux, macOS, or Cloud Shell)

   Save the request body in a file named request.json, and execute the following command:

   curl -X POST \
    -H "Authorization: Bearer $(gcloud auth print-access-token)" \
    -H "Content-Type: application/json; charset=utf-8" \
    -d @request.json \
    "https://iam.googleapis.com/v1/projects/PROJECT_ID/serviceAccounts/USER_SA_NAME@PROJECT_ID.iam.gserviceaccount.com:getIamPolicy"

   PowerShell (Windows)

   Save the request body in a file named request.json, and execute the following command:

   $cred = gcloud auth print-access-token
   $headers = @{ "Authorization" = "Bearer $cred" }
   Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://iam.googleapis.com/v1/projects/PROJECT_ID/serviceAccounts/USER_SA_NAME@PROJECT_ID.iam.gserviceaccount.com:getIamPolicy" | Select-Object -Expand Content

   APIs Explorer (browser)

   Copy the request body and open the method reference page. The APIs Explorer panel opens on the right side of the page. You can interact with this tool to send requests. Paste the request body in this tool, complete any other required fields, and click Execute.

   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 roleto the service agent.

   { "version": 1, "etag": "BwWl3KCTUMY=", "bindings": [ { "role": "roles/iam.serviceAccountTokenCreator", "members": [ "serviceAccount:SERVICE_AGENT_EMAIL" ] }, { "role": "roles/iam.serviceAccountUser", "members": [ "serviceAccount:SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com" ] } ]}

   Replace the following:

   • SERVICE_AGENT_EMAIL: The email address for theservice agent
   • SERVICE_ACCOUNT_NAME: The name of the user-managedservice account.
   • PROJECT_ID: The project ID where the user-managedservice account is located.

   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 projectID. Project IDs are alphanumeric strings, like my-project.
   • USER_SERVICE_ACCOUNT_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/SERVICE_ACCOUNT_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:SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com" ] } ] }}

   To send your request, expand one of these options:

   curl (Linux, macOS, or Cloud Shell)

   Save the request body in a file named request.json, and execute the following command:

   curl -X POST \
    -H "Authorization: Bearer $(gcloud auth print-access-token)" \
    -H "Content-Type: application/json; charset=utf-8" \
    -d @request.json \
    "https://iam.googleapis.com/v1/projects/PROJECT_ID/serviceAccounts/SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com:setIamPolicy"

   PowerShell (Windows)

   Save the request body in a file named request.json, and execute the following command:

   $cred = gcloud auth print-access-token
   $headers = @{ "Authorization" = "Bearer $cred" }
   Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://iam.googleapis.com/v1/projects/PROJECT_ID/serviceAccounts/SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com:setIamPolicy" | Select-Object -Expand Content

   APIs Explorer (browser)

   Copy the request body and open the method reference page. The APIs Explorer panel opens on the right side of the page. You can interact with this tool to send requests. Paste the request body in this tool, complete any other required fields, and click Execute.

   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" ] } ]}

   See Also

   Generate service account key in Google Cloud Platform (GCP)Connect to Google Cloud StorageCreate service accounts  |  IAM Documentation  |  Google CloudGive service account user permissions  |  Cloud Data Fusion Documentation  |  Google Cloud

Attach the service account to the new resource

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

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

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

To learn how to grant roles, seeGranting, 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 toa resource in another project. If you want to keep all of your service accountsin one project, you must update the organization policy for thatproject.

Enable service accounts to be attached across projects

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

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

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

  When this constraint is not enforced, IAM adds aproject lien that prevents the project from being deleted.This lien has the originiam.googleapis.com/cross-project-service-accounts. We strongly discourageyou from deleting this lien.

• Recommended: Ensure that theiam.restrictCrossProjectServiceAccountLienRemoval boolean constraint isenforced for the project.

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

To learn how to view or change a boolean constraint in an organizationpolicy, see Creating and managing organization policies.

Disable service accounts from being attached across projects

If you previously enabled service accounts to be attached acrossprojects, we strongly discourage you fromdisabling this feature, especially in production environments.

Specifically, in the project where your service accounts are located, youshouldn't make any of these changes:

• Don't update the project's organization policy to enforce theiam.disableCrossProjectServiceAccountUsage boolean constraint.
• Don't update the project's organization policy to not enforce theiam.restrictCrossProjectServiceAccountLienRemoval boolean constraint.
• Don't remove the project lien with the originiam.googleapis.com/cross-project-service-accounts, which prevents you fromdeleting the project.
• Don't delete the project.

If you are willing to accept the risk of disabling this feature, you can reduceyour risk by disabling the service accounts that you are usingacross projects, then monitoring your Google Cloud environment for issues.If you see any issues, you can re-enable the service accounts. Ifyou don't see any issues, then you might not have any Google Cloudresources that depend on a service account in a different project.

Audit logs for attaching service accounts

When a principal uses the iam.serviceAccounts.actAs permission to attach aservice account to a resource, IAM generates an audit log. Thisaudit log contains the following information:

• The email address of the principal that attached the service account to theresource
• Details about the service account that was attached to the resource

For a list of resources that you can attach service accounts to, see Attach theservice account to the new resource on this page.

For an example of this type of audit log, see Logs for using theiam.serviceAccounts.actAs permission. To learn more aboutaudit logs in general, see Cloud Audit Logs overview.

What's next

• Find out how to attach a service account to a Compute Engineinstance.
• Review and apply best practices for securing service accounts.
• Learn more about audit logging for IAM.