Nginx/Http 相关概念

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