What is the hard limit for the number of host projects to which a service project can attach?

In Google Cloud’s resource hierarchy, a service project can be attached to only one host project. This design is intended to maintain a clear and manageable structure, allowing for a more straightforward management of permissions, resources, and policies associated with the service project. By limiting the service project to a single host project, Google Cloud simplifies access controls and resource allocation, reducing the complexity that would arise from multiple overlapping host projects.

Understanding that a service project is designated as a subordinate within this hierarchy helps clarify the reasoning behind the hard limit. This hierarchical model is intrinsic to how Google Cloud enforces organization and structure across resources, ensuring that service projects remain coherent and consistent in their relationships with the host project.