IAM overview

This page describes how Google Cloud's Identity and Access Management (IAM) system works and how you can use it to manage access in Google Cloud.

IAM lets you grant granular access to specific Google Cloud resources and helps prevent access to other resources. IAM lets you adopt the security principle of least privilege, which states that nobody should have more permissions than they actually need.

How IAM works

With IAM, you manage access control by defining who (identity) has what access (role) for which resource. For example, Compute Engine virtual machine instances, Google Kubernetes Engine (GKE) clusters, and Cloud Storage buckets are all Google Cloud resources. The organizations, folders, and projects that you use to organize your resources are also resources.

In IAM, permission to access a resource isn't granted directly to the end user. Instead, permissions are grouped into roles, and roles are granted to authenticated principals. (In the past, IAM often referred to principals as members. Some APIs still use this term.)

An allow policy, also known as an IAM policy, defines and enforces what roles are granted to which principals. Each allow policy is attached to a resource. When an authenticated principal attempts to access a resource, IAM checks the resource's allow policy to determine whether the action is permitted.

The following diagram provides an example of permission management in IAM.

An allow policy with two role bindings. The role bindings associate specific principals with specific roles.

This model for access management has three main parts:

  • Principal. A principal represents an identity that can access a resource. Each principal has its own identifier.
  • Role. A role is a collection of permissions. Permissions determine what operations are allowed on a resource. When you grant a role to a principal, you grant all the permissions that the role contains.
  • Policy. The allow policy is a collection of role bindings that bind one or more principals to individual roles. When you want to define who (principal) has what type of access (role) on a resource, you create an allow policy and attach it to the resource.

In the preceding diagram, for example, the allow policy binds principals, such as user@example.com, to roles, such as the App Engine Admin role (roles/appengine.appAdmin). If the allow policy is attached to a project, the principals gain the specified roles within the project.

The rest of this page describes these concepts in greater detail.

In IAM, you grant access to principals, which represent an identity that can access a resource. In the context of access management, principals can be one of the following types:

For details about the identifier formats for each principal type, see Principal identifiers.

Google Accounts

A Google Account represents a developer, an administrator, or any other person who interacts with Google Cloud by using an account they created with Google. Any email address that's associated with a Google Account can be used as a principal, including gmail.com email addresses or email addresses with other domains. New users can sign up for a Google Account by going to the Google Account signup page.

Service accounts

A service account is an account for an application or compute workload instead of an individual end user. When you run code that's hosted on Google Cloud, you specify a service account to use as the identity for your application. You can create as many service accounts as needed to represent the different logical components of your application. For more information about using a service account to authenticate your application, see Service accounts.

Google groups

A Google group is a named collection of Google Accounts and service accounts. Every Google group has a unique email address that's associated with the group. You can find the email address that's associated with a Google group by clicking About on the homepage of any Google group. For more information about Google Groups, see the Google Groups homepage.

Google groups are a convenient way to apply access controls to a collection of users. You can grant and change access controls for a whole group at once instead of granting or changing access controls one at a time for individual users or service accounts. You can also add principals to or remove principals from a Google group instead of updating an allow policy to add or remove users.

Google groups don't have login credentials, and you cannot use Google groups to establish identity to make a request to access a resource.

Google Workspace accounts

A Google Workspace account represents a virtual group of all of the Google Accounts that it contains. Google Workspace accounts are associated with your organization's internet domain name, such as example.com. When you create a Google Account for a new user, such as username@example.com, that Google Account is added to the virtual group for your Google Workspace account.

Like Google groups, Google Workspace accounts cannot be used to establish identity, but they enable convenient permission management.

Cloud Identity domains

A Cloud Identity domain is like a Google Workspace account, because it represents a virtual group of all Google Accounts in an organization. However, Cloud Identity domain users don't have access to Google Workspace applications and features. For more information, see About Cloud Identity.

allAuthenticatedUsers

The value allAuthenticatedUsers is a special identifier that represents all service accounts and all users on the internet who have authenticated with a Google Account. This identifier includes accounts that aren't connected to a Google Workspace account or Cloud Identity domain, such as personal Gmail accounts. Users who aren't authenticated, such as anonymous visitors, aren't included.

This principal type doesn't include federated identities, which are managed by external identity providers (IdPs). If you use Workforce Identity Federation or Workload Identity Federation, don't use allAuthenticatedUsers. Instead, use one of the following:

Some resource types don't support this principal type.

allUsers

The value allUsers is a special identifier that represents anyone who is on the internet, including authenticated and unauthenticated users.

Some resource types don't support this principal type.

Federated identities in a workforce identity pool

A federated identity in a workforce identity pool is a user identity that is managed by an external IdP and federated by using Workforce Identity Federation. You can use a specific identity in a workforce identity pool, or you can use certain attributes to specify a group of user identities in a workforce identity pool. For information about principal identifiers for federated identities, see Principal identifiers.

Federated identities in a workload identity pool

A federated identity in a workload identity pool is a workload identity that is managed by an external IdP and federated by using Workload Identity Federation. You can use a specific workload identity in a workload identity pool, or you can use certain attributes to specify a group of workload identities in a workload identity pool. For information about principal identifiers for federated identities, see Principal identifiers.

GKE Pods

Workloads running on GKE use Workload Identity Federation for GKE to access Google Cloud services. For more information about principal identifiers for GKE Pods, see Reference Kubernetes resources in IAM policies.

Resource

If a user needs access to a specific Google Cloud resource, you can grant the user a role for that resource. Some examples of resources are projects, Compute Engine instances, and Cloud Storage buckets.

Some services support granting IAM permissions at a granularity finer than the project level. For example, you can grant the Storage Admin role (roles/storage.admin) to a user for a particular Cloud Storage bucket, or you can grant the Compute Instance Admin role (roles/compute.instanceAdmin) to a user for a specific Compute Engine instance.

In other cases, you can grant IAM permissions at the project level. The permissions are then inherited by all resources within that project. For example, to grant access to all Cloud Storage buckets in a project, grant access to the project instead of each individual bucket. Or to grant access to all Compute Engine instances in a project, grant access to the project rather than each individual instance.

For information on what roles can be granted on which resources, see Understanding roles and refer to the Lowest Resource column for a given role.

Permissions

Permissions determine what operations are allowed on a resource. In the IAM world, permissions are represented in the form of service.resource.verb, for example, pubsub.subscriptions.consume.

Permissions often correspond one-to-one with REST API methods. That is, each Google Cloud service has an associated set of permissions for each REST API method that it exposes. The caller of that method needs those permissions to call that method. For example, if you use Pub/Sub, and you need to call the topics.publish() method, you must have the pubsub.topics.publish permission for that topic.

You don't grant permissions to users directly. Instead, you identify roles that contain the appropriate permissions, and then grant those roles to the user. For a list of all available permissions and the roles that contain them, see the permissions reference.

Roles

A role is a collection of permissions. You cannot grant a permission to the user directly. Instead, you grant them a role. When you grant a role to a user, you grant them all the permissions that the role contains.

Permission to Role mapping.

There are several kinds of roles in IAM:

  • Basic roles: Roles historically available in the Google Cloud console. These roles are Owner, Editor, and Viewer.

  • Predefined roles: Roles that give finer-grained access control than the basic roles. For example, the predefined role Pub/Sub Publisher (roles/pubsub.publisher) provides access to only publish messages to a Pub/Sub topic.

  • Custom roles: Roles that you create to tailor permissions to the needs of your organization when predefined roles don't meet your needs.

For more information about roles, see the following resources:

Allow policy

When an authenticated principal attempts to access a resource, IAM checks the resource's allow policy to determine whether the action is allowed.

You can grant roles to users by creating an allow policy, which is a collection of statements that define who has what type of access. An allow policy is attached to a resource and is used to enforce access control whenever that resource is accessed.

IAM policy.

An allow policy consists of a list of role bindings. A role binding binds a list of principals to a role.

  • role: The role you want to grant to the principal. role is specified in the form of roles/service.roleName. For example, Cloud Storage provides the roles roles/storage.objectAdmin, roles/storage.objectCreator, and roles/storage.objectViewer, among others.

  • members: A list of one or more principals as described in the Concepts related to identity section in this document. Each principal type is identified with a prefix, such as a Google Account (user:), service account (serviceAccount:), Google group (group:), or a Google Workspace account or Cloud Identity domain (domain:). In the following example code snippet, the storage.objectAdmin role is granted to the following principals by using the appropriate prefix: user:my-user@example.com, serviceAccount:my-other-app@appspot.gserviceaccount.com, and group:my-group@example.com. The objectViewer role is granted to user:my-user@example.com.

The following code snippet shows the structure of an allow policy.

{
  "bindings": [
    {
      "role": "roles/storage.objectAdmin",
      "members": [
        "user:my-user@example.com",
        "serviceAccount:my-other-app@appspot.gserviceaccount.com",
        "group:my-group@example.com"
      ]
    },
    {
      "role": "roles/storage.objectViewer",
      "members": [
        "user:my-user@example.com"
      ]
    }
  ]
}

IAM and policy APIs

IAM provides a set of methods that you can use to create and manage allow policies on Google Cloud resources. These methods are exposed by the services that support IAM. For example, the IAM methods are exposed by the Resource Manager, Pub/Sub, and Cloud Life Sciences APIs, just to name a few.

The IAM methods are:

  • setIamPolicy(): Sets allow policies on your resources.
  • getIamPolicy(): Gets an allow policy that was previously set.
  • testIamPermissions(): Tests whether the caller has the specified permissions for a resource.

You can find the API reference topics for these methods in the documentation for each service that supports IAM.

Resource hierarchy

Google Cloud resources are organized hierarchically:

  • The organization is the root node in the hierarchy.
  • Folders are children of the organization, or of another folder.
  • Projects are children of the organization, or of a folder.
  • Resources for each service are descendants of projects.

Each resource has exactly one parent. For more information, see the Resource Manager resource hierarchy.

The following diagram is an example of a Google Cloud resource hierarchy.

Hierarchy for IAM resources.

You can set an allow policy at any level in the resource hierarchy: the organization level, the folder level, the project level, or the resource level. Resources inherit the allow policies of all of their parent resources. The effective allow policy for a resource is the union of the allow policy set on that resource and the allow policies inherited from higher up in the hierarchy.

This policy inheritance is transitive; in other words, resources inherit allow policies from the project, which inherit allow policies from folders, which inherit allow policies from the organization. Therefore, the organization-level allow policies also apply at the resource level.

For example, in the preceding diagram, topic_a is a Pub/Sub resource that lives under the project example-prod. As a result, if you grant the Editor role to a user on example-prod, you effectively grant the Editor role for topic_a to the user.

The allow policies for child resources inherit from the allow policies for their parent resources. For example, if you grant the Editor role to a user for a project, and grant the Viewer role to the same user for a child resource, then the user still has the Editor role grant for the child resource. If you change the resource hierarchy, the policy inheritance changes as well. For example, moving a project into an organization causes the project to inherit from the organization's allow policy.

IAM support for Google Cloud services

With IAM, every API method across all Google Cloud services is checked to ensure that the account making the API request has the appropriate permission to use the resource.

Google Cloud services offer predefined roles that provide fine-grained access control. For example, Compute Engine offers roles such as Compute Instance Admin and Compute Network Admin, and Cloud Storage offers roles such as Storage Folder Admin and Storage Object User.

Predefined roles are available for most Google Cloud services. For details, see the list of all predefined roles. If you need even more control over permissions, consider creating a custom role.

You can grant users certain roles to access resources at a granularity finer than the project level. For example, you can create an allow policy that grants a user the Subscriber role for a particular Pub/Sub topic. The list of all predefined roles shows the lowest-level, or finest-grained, type of resource that accepts each role.

Consistency model for the IAM API

The IAM API is eventually consistent. In other words, if you write data with the IAM API, then immediately read that data, the read operation might return an older version of the data. Also, changes you make might take time to affect access checks.

This consistency model affects how the IAM API works. For example, if you create a service account, then immediately refer to that service account in another request, the IAM API might say that the service account could not be found. This behavior occurs because operations are eventually consistent; it can take time for the new service account to become visible to read requests.

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