Understanding IAM custom roles

Cloud Identity and Access Management (Cloud IAM) provides predefined roles that give granular access to specific Google Cloud resources and prevent unwanted access to other resources.

Cloud IAM also provides the ability to create customized Cloud IAM roles. You can create a custom Cloud IAM role with one or more permissions and then grant that custom role to users. Cloud IAM provides a UI and API for creating and managing custom roles.

Key Point: Custom roles enable you to enforce the principle of least privilege, ensuring that the user and service accounts in your organization have only the permissions essential to performing their intended functions.

This topic does not provide a comprehensive list of all the Cloud IAM permissions you can include in your custom roles. To check whether a specific permission is supported in custom roles, see Support level for permissions in custom roles.

Before you begin

• Read the IAM Overview of basic Cloud IAM concepts.
• Read about the available IAM predefined roles.
• Understand the IAM best practices for least privilege.

Basic concepts

In Cloud IAM, you don't directly grant users permissions. Instead, you grant them roles, which bundle one or more permissions. There are three kinds of roles in Cloud IAM: primitive roles, predefined roles, and custom roles.

Primitive roles include three roles that existed prior to the introduction of Cloud IAM: Owner, Editor, and Viewer.

Predefined roles are created and maintained by Google. Their permissions are automatically updated as necessary, such as when new features or services are added to Google Cloud.

Custom roles are user-defined, and allow you to bundle one or more supported permissions to meet your specific needs. Custom roles are not maintained by Google; when new permissions, features, or services are added to Google Cloud, your custom roles will not be updated automatically.

Note: You can create a custom role at the organization level and at the project level. However, you cannot create custom roles at the folder level.

You create a custom role by combining one or more of the available Cloud IAM permissions. Permissions allow users to perform specific actions on Google Cloud resources. In the Cloud IAM world, permissions are represented in the form:

<service>.<resource>.<verb>

For example, the compute.instances.list permission allows a user to list the Google Compute Engine instances they own, while compute.instances.stop allows a user to stop a VM.

Permissions usually, but not always, correspond 1:1 with REST methods. That is, each Google Cloud service has an associated permission for each REST method that it has. To call a method, the caller needs that permission. For example, the caller of topic.publish() needs the pubsub.topics.publish permission.

Custom roles can only be used to grant permissions in policies for the same project or organization that owns the roles or resources under them. You cannot grant custom roles from one project or organization on a resource owned by a different project or organization.

Required permissions and roles

To create a custom role, a caller must have the iam.roles.create permission.

Users who are not owners, including organization administrators, must be assigned either the Organization Role Administrator role (roles/iam.organizationRoleAdmin) or the IAM Role Administrator role (roles/iam.roleAdmin). The IAM Security Reviewer role (roles/iam.securityReviewer) enables the ability to view custom roles but not administer them.

The custom roles user interface is in the Google Cloud Console under IAM Roles. It is only available to users who have permissions to create or manage custom roles. By default, only project owners can create new roles. Project owners can control access to this feature by granting IAM Role Administrator role to others on the same project; for organizations, only Organization Administrators can grant the Organization Role Administrator role.

The administrative roles are described in more detail below.

Organization Role Administrator role

If you have an organization associated with your GCP account, the Organization Role Administrator role enables you to administer all custom roles in your organization. This role can only be granted at the organization level. Only Organization Administrators can grant the Organization Role Administrator role.

The following table lists the permissions in the Organization Role Administrator role:

Role	Permissions
roles/iam.organizationRoleAdmin	iam.roles.create iam.roles.delete iam.roles.undelete iam.roles.get iam.roles.list iam.roles.update resourcemanager.projects.get resourcemanager.projects.getIamPolicy resourcemanager.projects.list resourcemanager.organizations.get resourcemanager.organizations.getIamPolicy

Role Administrator role

The Role Administrator role enables you to administer all custom roles for a project. Use this role if you do not have an organization. This role can only be granted at the project level by project or organization owners.

The following table lists the permissions in the Role Administrator role:

Role	Permissions
roles/iam.roleAdmin	iam.roles.create iam.roles.delete iam.roles.undelete iam.roles.get iam.roles.list iam.roles.update resourcemanager.projects.get resourcemanager.projects.getIamPolicy

Custom roles lifecycle

There are a few concepts that apply when deciding how to model, create, and manage your custom roles.

Creation

Before you decide to create a custom role, check whether the service has a predefined role—or a combination of multiple predefined roles—that meets your needs. For a complete list of predefined roles, as well as the permissions that are included in each predefined role, see the predefined roles reference.

If there is no predefined role—or combination of predefined roles—that meets your needs, you can create a custom role that includes only the permissions you need to grant. For details, see Creating and managing custom roles.

Unsupported or unavailable permissions

Some permissions might not be visible to you or usable in a custom role. For example, a permission might not be available for use in custom roles if the service is in beta, or if you have not enabled the API for the service.

To check whether you can use a specific permission in custom roles, see Support level for permissions in custom roles. To check which permissions you can use with a specific resource, see Viewing the available permissions for a resource.

The following Cloud IAM permissions are not supported in custom roles:

• iam.serviceAccounts.getAccessToken
• iam.serviceAccounts.actAs
• iam.serviceAccounts.signBlob
• iam.serviceAccounts.signJwt

Permission dependencies

Some permissions are effective only when granted in pairs. For example, to update a Cloud IAM policy, you must use the read-modify-write pattern. As a result, to update a policy, you almost always need the getIamPolicy permission for that service and resource type, in addition to the setIamPolicy permission.

Naming the role

The ID for a custom role must be unique. It can be up to 64 characters long and comprised of uppercase and lowercase alphanumeric characters, underscores, and periods.

The title for a custom role does not have to be unique. Therefore, the Cloud Console could display more than one custom role with the same title. To avoid confusion, use unique and descriptive titles for your custom roles. Titles can be up to 100 bytes long and can contain uppercase and lowercase alphanumeric characters and symbols. Role titles can be changed at any time.

Choose the ID of your role carefully, because it cannot be changed. You can delete a role, but you can't create a new custom role with the same ID until after the 37-day deletion process has completed. For more information about the deletion process, see Deleting a custom role.

The role title is what is displayed in the Cloud Console. Choose unambiguous titles to prevent confusion for users selecting custom roles in the Cloud Console. Also consider indicating which roles are organization-level vs. project-level by putting that information in the role title.

Role description

Consider updating the role description after editing a custom role, and include both the date it was modified and a summary of the intended purpose for the role. Descriptions can be up to 256 characters long and comprised of uppercase and lowercase alphanumeric characters and symbols.

Testing and deploying

Custom roles include a role.stage property. Initially, set the stage to ALPHA to indicate that the role is in early development and not ready for production. Then, allow a small set of members of your organization to use the role in a few sample use cases.

When the members are happy with the newly created custom role, change the role.stage property to BETA or GA. In general, if your custom role references permissions for services that are in Beta, you should mark it BETA, not GA, until the service is out of Beta.

Maintenance

Job functions and product functionality are constantly evolving. Keeping custom roles up-to-date and assigned the least privileges necessary requires maintenance effort.

For example, when a released service gets new Beta features, those API methods become publicly available and the permissions are automatically added to the corresponding primitive and predefined roles. Your custom roles for that service do not inherit those new permissions, so users assigned to those custom roles may report that they cannot access the new Beta features. At that point, you could choose to add them, or perhaps create a separate custom role to only grant certain users access to those Beta features.

While Google may update an existing predefined role by adding (or removing) permissions, we do not modify custom roles based on the predefined roles. Custom roles are flat lists of permissions; there is no link to the predefined role(s) it may have been based on.

We recommend adding these details to the description field for an existing custom role to make it easier to review whether recent changes to predefined roles warrant updates to your custom role. The Cloud Console automatically puts that information in the description when creating a new custom role.

Refer to the IAM Permissions Change Log to determine what permissions have changed recently.

Disabling custom roles

If you no longer wish for people in the your organization to use the role, change its role.stage property to DEPRECATED, and optionally set the deprecation_message to let users know what alternative roles should be used or where to get more information. You should also make sure that you don't have any policies in your organization that might still be referencing the deprecated role.

When you're sure that the role can be disabled, call roles:UpdateRole() to disable this role.

Known limitations

• Some predefined roles contain permissions that are not permitted in custom roles. To check whether you can use a specific permission in a custom role, see Support level for permissions in custom roles.
• Custom roles created within a project can't list other projects. When you copy a predefined role that includes the resourcemanager.projects.list permission into a new project-level custom role, one of the following messages will be displayed:
  • Cloud Console: The following warning message is displayed: "Not applicable for project-level custom roles". The resourcemanager.projects.list permission will be automatically unselected from the list of included permissions, and you can proceed with creating the role.
  • Cloud SDK gcloud command-line tool: The following error message is returned: INVALID_ARGUMENT: Permission resourcemanager.projects.list is not valid. The custom role will not be created until you first remove the resourcemanager.projects.list permission from the role definition and try the operation again.
  • Google Cloud APIs: The following error message is returned: Permission resourcemanager.projects.list is not valid, along with an HTTP 400 error code and a status of INVALID_ARGUMENT. The custom role will not be created until you first remove the resourcemanager.projects.list permission from the role definition and try the operation again.

What's next

Learn how to create custom roles.