Nginx reverse proxy

Hello,
I am tried to configure my nginx that is installed on Ubuntu 16.10
I have the following infrastructure

wan
|
nginx reverse proxy with domain ssl.example.com
|
web server http.example.com


the http.example.com is point to ssl.example.com ip address

when the client open http://http.example.com it should be redirect to https://http.example.com directly
the client will establish ssl with my reverse proxy ssl.example.com "I already have installed lets encrypt cert"
my reverse proxy should be request the http.example.com -with no ssl -

it's like a cloud flare.

so what the configuration I should be do it ?
also how I can load balance to too web server that is in back of reverse proxy.
thanks.