Ed W <lists@xxxxxxxxxxxxxx> wrote on 10/31/2012
09:03:14:
>
> On 31/10/2012 10:36, Tomalak Geret'kal wrote:
> > On 31/10/2012 10:35, Miroslav Lichvar wrote:
> >> On Wed, Oct 31, 2012 at 10:14:01AM +0000, Tomalak Geret'kal
wrote:
> >>> Again, chrony doesn't need the TTL. Caching is handled
by the
> >>> resolver.
> >>> getaddrinfo() blocking is a more concrete problem to
solve - good
> >>> spot.
> >> I don't think getaddrinfo() does any caching, that has to
be done in
> >> nscd or a local DNS server.
> >>
> > I didn't claim otherwise!
> >
> > Tom
>
> Then you need to be very careful that millions of routers out there
> don't suddenly start issuing DNS requests every few seconds because
> someone upgraded a firmware to include this new version of chrony
and
> didn't notice the change in behaviour (not all chinese/taiwanese router
> board builders will read the english release notes...)
Please don't let me get blamed for starting that avalanche!
:-)
> Remember unlike windows its much more normal to not have any dns caching
> on linux and rely on the nearest upstream (hopefully inside your
> infrastructure)
My distros (Fedora and previously RHL) have done local
caching for as long as I can remember. I'd be surprised to see one
that doesn't actually.
> I see that this is a very dangerous change.
I'm inclined to agree with this now.
I posted the Q because chrony's behavior seemed at odds with most
network services, but I can clearly see now there are some very good reasons
for that. In our case, we've got our own internal radio-clock server
so we're not using pool.ntp.org, but I certainly realize many installs
our going to be pointing to some round-robin DNS setup.
IMHO I think the best strategy forward
would be just leave things as they are, but perhaps add some warnings to
the documentation and perhaps even run-time logs that the name resolution
is a one-time deal. Run-time warnings could even point the user to
a specific part of the docs explaining what was learned in this discussion.
In any case, I very much appreciate
everyone's effort to make it better and/or explain the devil in the details.
Thank you all.
--
John Florian