What is Upstream and Downstream services in a Micro-service based architecture?

The downstream services are the ones that consume the upstream service. In particular, they depend on the upstream service. More generally, upstream services don't need to know or care about the existence of downstream services. Downstream services care about the existence of upstream services, even if they only optionally consume them.

http://reflectoring.io/upstream-downstream

Definition 1: The direction of action

Upstream: receiving requests from / sending responses to

• A service upstream is calling me.

Downstream: making requests to / receiving responses from

• I am calling a service downstream.

Definition 2: The direction of dependency

Upstream: making requests to / receiving responses from

• I am calling a service upstream.

Downstream: receiving requests from / sending responses to

• A service downstream is calling me.

So,

There are resources on the internet which support both of these definitions. Maybe we will resolve this question one day, but for now the answer is: it's either.