The real question: To get sticky-cookie functionality, is it necessary to use nginx commercial subscription?
This doc seems to indicate yes: http://nginx.org/en/docs/http/ngx_http_upstream_module.html#sticky (note the tag at the bottom of the entry for "sticky" keyword)
But this doc makes the upstream functionality appear included: http://nginx.org/en/docs/http/ngx_http_upstream_module.html
I am getting confused. It appears that the upstream module is part of the FOSS flavor, but some directives require commercial subscription? (And "sticky" is a directive that requires commercial subscription?)