feat(upstream) add host_header to upstream entities

[locao]

Add support to hostname attribute in upstream entities.

This attribute is used as the Host header when proxying requests through Kong. It takes precedence over the Host that clients send to Kong.

[hbagdi]

Question: Will active HTTP health-check set the host header to this new property (if present) as well?

[locao]

Will active HTTP health-check set the host header to this new property (if present) as well?

No, it won't. I will change this behavior, thanks for pointing that, @hbagdi!

[Tieske]

This change doesn't make sense to me.

afaik we have 2 possible values for the upstream host-header; the incoming host-header, or the hostname of the upstream server.

This subject is complicated because we do not cleanly separate teh construction of the upstream request in our flow. As mentioned elsewhere; we need to collect info in pre-access phase and only build teh upstream properties in post-access.

Adding this extra property only makes thing more complicated imo.

In pseudo code:

-- pre-access
host_header_incoming = request.headers["Host"]
host_header_upstream = nil
host_header_preserve = route.preserve_hostname

-- pdk
function set_upstream_host_header(name)
  host_header_upstream = name
end
function set_host_preserve(bool)
  host_header_preserve = bool
end

--post-access
ip, port, resolved_name = dns.resolve()  -- includes balancers, returns hostname resolved, or target name if balancer

host_header_upstream = host_header_upstream or
                       (host_header_preserve and host_header_incoming) or
                       resolved_name

Does this make sense?

[hishamhm]

Nice, getting there! Left a couple of suggestions.

[hishamhm]

Can you make this a value other than localhost, some invalid name like upstream-hostname.test to make sure this test does not use the underlying system's name resolution in any way?