"Upstream" vs. "Downstream" Terminology

[nate-martinez]

Hi folks,

I have a general question about the use of "upstream" vs "downstream" in the Pingora docs. In pingora/docs/quick_start.md, the docs refer to the set of servers being proxied by Pingora as the "upstream" IPs.

What confuses me about this is that I'm used to thinking of servers behind a load balancer (and closer to the database) as being "downstream" from the perspective of the client - the client's request comes in, and it flows all the way to the DB.

Could someone explain the intuition for why "upstream" as used in the Pingora docs is correct? Why are we calling the servers behind the LB as "upstream" from the perspective of either the client or the LB?

Thanks in advance!