Re: issue 381: Discovery of the support of the HTTP2 protocol: DNS-based Upgrade

Hi,

On 19 Feb 2014, at 12:02 pm, William Chan (陈智昌) <willchan@chromium.org> wrote:

>> A strong +1 for mandating SRV for HTTP/2.x discovery, because:
> 
> I'm open to speccing out SRV for HTTP/2 and potentially using it. But
> I think mandating it is silly.

Ah, yes. To clarify in standards language: I think support for SRV
lookup in clients is a MUST not a MAY, and for the hosting setup
probably a SHOULD[1].

I also think it should be preferred, that is, the raw IPv4 and IPv6
address record queries should be tried only after a query for SRV
records has failed - and yes this means hosting providers who don’t
adopt SRV in their DNS will bear the burden of a triple, rather
than a single lookup.

Note that this semantic has precedent - it is how the transition
to MX records for email delivery was made and is called the “implicit
MX” rule. I think HTTP/2.x should have a similar “implicit SRV”
rule as the wise way to define the behaviour. See RFC5321 s5.1.

So the positive incentive is declarative DNS support for h2 upgrade,
which conveniently also supplies adequate support at last for IPv6,
apex naked domains, alternative ports and the other benefits of
SRV[2]. And performance becomes a stick to drive the adoption
donkey.[3]


> It's not immediately clear to me the extent to switch you are pushing
> back on A record use. Do you think in-band discovery (well,
> advertisement) via TLS-ALPN or HTTP Upgrade are acceptable mechanisms?

Yes. I'm not suggesting those should be out.


regards
Josh.


[1] This is a compromise. If one were designing a new protocol with
no legacy concerns then I would strongly push for SRV as the only
acceptable DNS record type for server discovery.

[2] Fallback server & weighted-round-robin if you want them.

[3] I know Eliot has expressed concerns about both future-proofing
for h3, and for resolver performance at the <10% of sites that have
zone cuts at _tcp.example.com in their public DNS. However, I think
those are both manageable issues and do not outweigh the benefits
of a DNS record that is immediately supported by practically all
servers & hosting providers, and that solves several other lingering
problems right off the bat.

Received on Thursday, 27 February 2014 19:21:33 UTC