What is the difference between GRPC and HTTP?

HTTP (Hypertext Transfer Protocol) is a stateless protocol primarily used for website and web application requests over the internet.
gRPC (gRemote Procedure Call) is a modern, open-source communication protocol from Google that uses HTTP/2 for transport, protocol buffers as the interface description language, and provides features like bi-directional streaming, multiplexing, and flow control.

gRPC is more efficient in a tracing context than HTTP, but HTTP is more widely supported. Phoenix can send traces over either HTTP or gRPC.