While I am configuring my nginx, I found two modules: ngx_http_limit_conn_module and ngx_http_limit_req_module one is for limiting connection per defined key, and one for limiting request.
My question is what is the relationship (and difference) between a HTTP connection and a request. It seems that multiple HTTP requests can use one common HTTP connection, what is the principle under this?
Basically connections are established to make requests using it. So for instance endpoint for given key may accept 5 connections per hour from given IP address. But it doesn't mean only 5 requests can be made but much more - if the connection is not closed after a request (from HTTP 1.1 it's by default kept alive).
E.g. an endpoint accepts 5 connections and 10 requests from given IP address. If connection is established for every request only 5 requests overall can be made. If connection is kept alive single client may make all the requests. If there are 5 clients, every establishes a connection and keeps it alive there are 2 request approx. that can be made by each client - however one can make all the request if it's fast enough.