There are many web-service/app which serves bitcoin. What is their tech prototype ?
As my understanding, they must enter bitcoin network by a node. How do they provide service on internet ? I guess they talk to some bitcoin core node by rest/RPC by IP address and then expose their service by web interface.
They run Bitcoin Core as part of their backend. Their APIs and whatever else is part of their service accesses the RPCs as needed. The RPCs are never directly exposed to the internet.