3 quick questions

Hi there-

I had 3 questions about nginx functionality:

a) suppose I have a location block in which I'd like to trigger some sort of script or 'notify' another location...would the best way be to use the HttpLuaModule, and execute a script within the location block? Or is there a simpler way?

b) I'd like to do a setup where a single nginx is handling 4 other nginx nodes in a round-robin fashion. This will be to load-balance SSL encryption, where the first hop (I assume with proxy_pass being the best way) is not secure, but each individual node handles it's own separate SSL encryption.
See the crude image attached...basically A/B/C/D are duplicate locations /generally identical ,and each handle the request made by the initial node separately, and then fan out as appropriate.

c) On the topic of b), is there a way for a location to 'know' where it was referenced from? For example, if I got to this location from location X, I'd like to enforce SSL encryption, but from location Y, encryption is not necessary etc.

Thanks, and apologies if these questions are vague...still super new.