On Sun, Jul 24, 2011 at 08:28:49PM +0200, Iñaki Baz Castillo wrote:
2011/7/24 Willy Tarreau <w(_at_)1wt(_dot_)eu>:
And I'm really tired of hearing the argument of the "latency" which
nobody demostrates (but just talks about it without replying me how
the same is not a problem in realtime protocols like SIP and XMPP).
Because you have never worked in a mobile phone environment. You'd be
amazed to see what end users are paying for ! Count 300-500 ms on average
for a DNS request.
Well, mobile phone world is a pain due to GPRS/3G internet
connections. But those networks should be improved rather than
assuming that all the Internet must change to work on those infernal
environments (which IMHO are not yet ready for modern internet). All I
see in mobile networks are workarounds.
Those are infernal but part of the time cannot be compressed much more
due to the fact that you have to share the medium with many other people
and you have to wait for your slot to send packets. And I'm not even
counting the time it can take to forward your data across the country
between the antenna and the datacenter. Sure things will improve, but
I don't expect seeing anything below 40-50ms.
Could you explain me why DNS A is good but DNS SRV is bad in such
"anarchic" deployments?
DNS is not mandatory for HTTP. It's not "DNS A" which makes it good, but
"no mandatory DNS". This is a huge difference.
So, do you mean using URI's with IP rather than domain? (take into
account that TLS connection require the certificate to match the URI
domain, but anyhow it's also possible to use IP's within the
certificate).
On internal networks, using IP instead of URIs is not uncommon at all,
especially on developer networks where you need many instances of the
same server in different versions or for different people. Some static
servers also make use of this because it saves one roundtrip. And of
course you have it on your ADSL router's web-based configuration interface
otherwise you wouldn't be able to contact the DNS to reach the router :-)
But that's not what I meant, I meant that DNS is not the only solution
to resolve host names. WINS, NIS and /etc/hosts are usable too. When I
was a student in 94, we had all our passwords and hostnames in NIS and
no DNS was configured. It worked like a charm. DNS is not something
mandatory at all for many protocols. It just happens to be the standard
over the public Internet.
Regards,
Willy
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