On Mon, Jun 1, 2015 at 1:42 PM, drago01 <drago01(a)gmail.com> wrote:
On Mon, Jun 1, 2015 at 9:28 PM, Andrew Lutomirski
<luto(a)mit.edu> wrote:
> On Mon, Jun 1, 2015 at 12:25 PM, Ryan S. Brown <ryansb(a)redhat.com> wrote:
>> On 06/01/2015 01:55 PM, Jason L Tibbitts III wrote:
>>>>>>>> "RSB" == Ryan S Brown <ryansb(a)redhat.com>
writes:
>>>
>>> RSB> I disagree; for server & cloud deployments it doesn't make
sense to
>>> RSB> duplicate a DNS server on *every* host, and if you care about
>>> RSB> DNSSEC you likely already run a trusted resolver.
>>>
>>> I disagree generally in the case of server deployments.
>>>
>>> Having a local caching resolver is pretty much essential, even though we
>>> all know it's just a workaround for glibc.
>>>
>>> Basically, if you have properly functioning DNS on multiple local
>>> servers but not having anything fancier like heartbeat-based IP handoff
>>> or a load balancing appliance or something, and the first resolver in
>>> resolv.conf goes offline, your hosts are screwed. glibc's resolver code
>>> is simply horrible. This is completely exclusive of DNSSEC issues.
>>
>> I don't think it's essential for either the server or the cloud product.
>> Servers run in a much more reliable network than your average SOHO or
>> coffee shop setup, and their behavior with regard to DNS doesn't need a
>> local caching resolver. LAN DNS (probably with split horizon for
>> DC-internal services) is plenty fast and reliable, there isn't a need to
>> run a zillion instances of Unbound.
>
> I agree it's not essential for a server, but it can be quite helpful
> to work around glibc bugs. For example, I've hit
>
https://sourceware.org/bugzilla/show_bug.cgi?id=17802 several times in
> production. Yes, that's a glibc bug, and glibc should fix it.
> Nonetheless, bugs like that wouldn't matter as much if there were a
> local resolver.
That's not how bugs should be dealt with ... if there is a bug it
should be fixed where it is not duct taped this way.
This is glibc we're talking about, though. Have you tried to get a
glibc bug fixed? It's not a pleasant experience.
For example, the bug I reported has a candidate patch. That patch
isn't applied, and the patch looks like the bug might be a security
issue. It's been in that state for months. This is not unusual for
glibc.
Anyway, even on a LAN, the overhead of a network round trip per
cacheable DNS query may be non-negligable for some use cases. A local
caching resolver fixes that, too.
--Andy