head is an inexpensive way to find out about some
servier that you're looking to hack, i mean,
connect with.
the caller's ip address - if not spoofed - should
be available in nginx's logs. but it will probably
only tell you the address of the last proxy being
used by the caller (from within a chain of proxies).
head is a valid http request of and by itself;
there is no other "request" attached to it. it's simply
one of the many, many probes for an outward-
facing server.