GCP - Service Account vs Service Agent

Service Agent is one kind of Service Account. Service Account can be:

• User-managed Service Account:
  • managed by users.
  • the identity of the workload in GCP.
  • for user owned resources accessing other GCP resources.
  • for example, user owns a GCE instance and a GCS bucket, a service account can be attached to the GCE instance, it will be used to authn and authz when writting to the GCE bucket.
  • format: [email protected]; 1234 is the project id, it is on the right side of @, indicates that it is owned by this user project.
• Service Agent:
  • managed by Google Cloud.
  • allowing GCP services to access resources on your behalf.
  • for example, user owns a GCS bucket; Cloud Logging want to write logs to the bucket, it can use a service agent to get access.
  • format: [email protected]; 5678 is the org id, it is on the left side of @ indicates it is not the owner; CIEM is on the right side, so this is a CIEM service agent for the org 5678.

Note:

• for per-project service agents, even though Service Agents are actually service accounts owned by a producer project owned by Google, GCP infrastructure treats them as if they were owned by their associated consumer resource.
• service agents are using the new format service-{project-number|org-id}@{service}.iam.gserviceaccount.com, which specifies both the GCP service (on the right side of @), and the customer resource container (on the left side of @); the following legacy types of service accounts are no longer used:
  • Cloud Service Robot: one SA for all services to access one customer project {projectnumber}@cloudservices.gserviceaccount.com
  • one SA for a service to access all customer projects: {servicename}@system.gserviceaccount.com
• service agent: service
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