This page explains service accounts, types of service accounts, and the IAM roles that are available to service accounts.
Before you begin
- Understand the basic concepts of Cloud IAM.
What are service accounts?
For example, a Compute Engine VM may run as a service account, and that account can be given permissions to access the resources it needs. This way the service account is the identity of the service, and the service account's permissions control which resources the service can access.
A service account is identified by its email address, which is unique to the account.
Differences between a service account and a user account
Service accounts differ from user accounts in a few key ways:
- Service accounts do not have passwords, and cannot log in via browsers or cookies.
- Service accounts are associated with private/public RSA key-pairs that are used for authentication to Google.
- Cloud IAM permissions can be granted to allow other users (or other service accounts) to impersonate a service account.
- Service accounts offer higher service-level objectives (SLOs) than user accounts when authenticating to GCP, ensuring reliable service for applications that use them.
- Service accounts are not members of your G Suite domain, unlike user accounts. For example, if you share assets with all members in your G Suite domain, they will not be shared with service accounts. Similarly, any assets created by a service account cannot be owned or managed by G Suite admins.
Service account keys
Each service account is associated with two sets of public/private RSA key pairs that are used to authenticate to Google: Google-managed keys, and user-managed keys.
Google-managed key pairs imply that Google stores both the public and private portion of the key, rotates them regularly (each key can be used for signing a maximum of two weeks), and the private key is always held in escrow and is never directly accessible. Cloud IAM provides APIs to use these keys to sign on behalf of the service account. See Creating Short-lived service account credentials for more information.
User-managed key pairs imply that you own both the public and private portions of a key pair. You can create one or more user-managed key pairs (also known as "external" keys) that can be used from outside of GCP. Google only stores the public portion of a user-managed key.
The private portion of a user-managed key pair is most commonly used with Application Default Credentials. The private key is then used to authenticate server-to-server applications.
For user-managed keys, you are responsible for security of the private key and
other management operations such as key rotation. User-managed keys can be
managed by the Cloud IAM API,
tool, or the service accounts page in the GCP Console. You can create
up to 10 service account keys per service account to facilitate key rotation.
Consider using Cloud Key Management Service (Cloud KMS) to help securely manage your keys.
Preventing user-managed keys
User-managed keys are extremely powerful credentials, and they can represent a security risk if they are not managed correctly.
You can limit their use by applying the
constraints/iam.disableServiceAccountKeyCreation Organization Policy Constraint
to projects, folders, or even your entire organization. After applying the
constraint, you can enable user-managed keys in well-controlled locations to
minimize the potential risk caused by unmanaged keys.
Types of service accounts
User-managed service accounts
When you create a new Cloud project using GCP Console and if Compute Engine API is enabled for your project, a Compute Engine Service account is created for you by default. It is identifiable using the email:
If your project contains a App Engine application, the default App Engine service account is created in your project by default. It is identifiable using the email:
If you create a service account in your project, you'll name the service account and it will be assigned an email with the following format:
You can create up to 100 service accounts per project (including the default
Compute Engine service account and the App Engine service account)
using the IAM API, the GCP console, or the
tool. These default service accounts and the service accounts you explicitly
create are the user-managed service accounts.
Google-managed service accounts
In addition to the user-managed service accounts, you might see some additional service accounts in your project's IAM policy or in GCP Console. These service accounts are created and owned by Google. These accounts represent different Google services and each account is automatically granted IAM roles to access your GCP project.
Google APIs service account
An example of a Google-managed service account is a Google API service account identifiable using the email:
This service account is designed specifically to run internal Google processes on your behalf and is not listed in the Service Accounts section of GCP Console. By default, the account is automatically granted the project editor role on the project and is listed in the IAM section of GCP Console. This service account is deleted only when the project is deleted. Google services rely on the account having access to your project, so you should not remove or change the service account's role on your project.
Service account permissions
For instance, Alice can have the editor role on a service account and Bob can have viewer role on a service account. This is just like granting roles for any other GCP resource.
The default Compute Engine and App Engine service accounts are granted editor roles on the project when they are created so that the code executing in your App or VM instance has the necessary permissions. In this case the service accounts are identities that are granted the editor role for a resource (project).
If you want to allow your automation to access a Cloud Storage bucket, you grant the service account (that your automation uses) the permissions to read the Cloud Storage bucket. In this case the service account is the identity that you are granting permissions for another resource (the Cloud Storage bucket).
The Service Account User role
You can grant the Service Account User role (
the project level for all service accounts in the project, or at the service
Granting the Service Account User role to a user for a project gives the user access to all service accounts in the project, including service accounts that may be created in the future.
Granting the Service Account User role to a user for a specific service account gives a user access to only that service account.
Users granted the Service Account User role on a service account can use it to
indirectly access all the resources to which the service account has access. For
example, if a service account has been granted the Compute Admin role
roles/compute.admin), a user that has been granted the Service Account Users
roles/iam.serviceAccountUser) on that service account can act as the
service account to start a Compute Engine instance. In this flow, the
user impersonates the service account to perform any tasks using its granted
roles and permissions.
For more information on granting users roles on service accounts, see Configuring ownership and access to a service account.
Service accounts represent your service-level security. The security of the service is determined by the people who have Cloud IAM roles to manage and use the service accounts, and people who hold private external keys for those service accounts. Best practices to ensure security include the following:
- Use the Cloud IAM API to audit the service accounts, the keys, and the policies on those service accounts.
- If your service accounts don't need external keys, delete them.
- If users don't need permission to manage or use service accounts, then remove them from the applicable Cloud IAM policy.
To learn more about best practices, see Understanding service accounts.
The Service Account Token Creator role
This role enables impersonation of service accounts to create OAuth2 access tokens, sign blobs, or sign JWTs.
The Service Account Actor role
This role has been deprecated. If you need to run operations as the service account, use the Service Account User role. To effectively provide the same permissions as Service Account Actor, you should also grant Service Account Token Creator.
Access scopes are the legacy method of specifying permissions for your VM. Before the existence of IAM roles, access scopes were the only mechanism for granting permissions to service accounts. Although they are not the primary way of granting permissions now, you must still set access scopes when configuring an instance to run as a service account. For information on access scopes see Google Compute Engine documentation
Short-Lived Service Account Credentials
You can create short-lived credentials that allow you to assume the identity of a GCP service account. These credentials can be used to authenticate calls to Google Cloud Platform APIs or other non-Google APIs.
The most common use case for these credentials is to temporarily delegate access to GCP resources across different projects, organizations, or accounts. For example, instead of providing an external caller with the permanent credentials of a highly-privileged service account, temporary emergency access can be granted instead. Alternatively, a designated service account with restricted permissions can be impersonated by an external caller without requiring a more highly-privileged service account's credentials.
For more information, see Creating Short-Lived Service Account Credentials.
Application Default Credentials
Application default credentials are a mechanism to make it easy to use service accounts when operating inside and outside GCP, as well as across multiple GCP projects. The most common use case is testing code on a local machine, and then moving to a development project in GCP, and then moving to a production project in GCP. Using Application Default Credentials ensures that the service account works seamlessly; when testing on your local machine, it uses a locally-stored service account key, but when running on Compute Engine, it uses the project's default Compute Engine service account. See Application Default Credentials for more information.
For best practices on using service accounts, see Understanding Service Accounts.
Read the following guides to understand how to: