Resolver, AWS ELB and proxy_pass

Morning,
I am confused about proxy_pass, AWS ELB and the resolver directive. Do I still need to use a variable and resolver in my proxy_pass, or can I simply add a resolver directive?

All posts so far state that I have to use both a variable and a resolver to ensure that it always obeys the AWS TTL.

Also some posts are saying that I need to add valid=xxs to ensure it works. I understand that this would simply ensure that the cached entry is looked up more frequently, but is it a requirement to assist with AWS ELB.

Any help would be appreciated.

Nicholas Irving