Just general curiousity, and I haven't been able to find any information on it.

I've recently started learning about microservices and what surrounds them, such as API gateways. I understand that an API gateway can be a single entry point for a web application or such. But if there are multiple services, each having its own set (and shared?), would they all be under one big API gateway (for shared authorization, authentication, access control etc), or would they have one gate way each?