Re: p1: Via and gateways

Willy Tarreau <w@1wt.eu> Sat, 20 April 2013 06:51 UTC

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Date: Sat, 20 Apr 2013 08:51:05 +0200
From: Willy Tarreau <w@1wt.eu>
To: Mark Nottingham <mnot@mnot.net>
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Subject: Re: p1: Via and gateways
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On Sat, Apr 20, 2013 at 04:44:30PM +1000, Mark Nottingham wrote:
> 
> On 20/04/2013, at 4:23 PM, Willy Tarreau <w@1wt.eu> wrote:
> 
> > On Sat, Apr 20, 2013 at 02:07:11PM +1000, Mark Nottingham wrote:
> >> 
> >> p1 Section 2.3 says:
> >> 
> >>> However, an HTTP-to-HTTP gateway that wishes to interoperate with third-party HTTP servers must conform to HTTP user agent requirements on the gateway's inbound connection and must implement the Connection (Section 6.1) and Via (Section 5.7.1) header fields for both connections.
> >> 
> >> This means that accelerators and CDNs MUST generate a Via header on the outbound connection. This isn't widely practiced, and I'm not sure it's necessary. Comments?
> > 
> > I know no load-balancer which does it anyway. Especially in hosted
> > environments where it is desired that the infrastructure is as much
> > transparent to the hosted servers as possible.
> > 
> > I must say I never understood the rationale behind Via because for
> > incoming traffic we don't care and for outgoing traffic we don't
> > want to disclose to the world our inside details.
> 
> Yes. It makes sense for proxies, so that the endpoints can discover the
> capabilities of the whole path. I'm not convinced that applies to gateways,
> because they're taking the responsibility of the origin server.

But are client and servers really making use of the Via header to discover
this ?

My impression is that nowadays proxies tend to build messages looking the
closest to what they receive and will either mimmick the HTTP version of
the proxied request, or arrange for the required conversions (eg: chunked-
encoding to content-length or close).

I think Amos might have some experience on this.

Willy