1.upstream
upstream/downstream: ????( Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream.)
According to this definition:
1.if you are looking at a request, then the client is upstream, and the server is downstream;
2.in contrast, if you are looking at a response, then the client is downstream, and the server is upstream.
In HTTP most of the data flow is not for requests, but for responses.
参考: https://tools.ietf.org/html/rfc2616#section-1.3
Nginx/Http 相关概念
原文地址:https://www.cnblogs.com/dinglin1/p/9063548.html