dns and software, was Re: Reliable Cloud host ?

Thu Mar 1 16:58:57 UTC 2012

On Thu, Mar 1, 2012 at 10:01 AM, Michael Thomas <mike at mtcc.com> wrote:
> On 03/01/2012 06:26 AM, William Herrin wrote:
>> The even simpler approach: create an AF_NAME with a sockaddr struct
>> that contains a hostname instead of an IPvX address. Then let
>> connect() figure out the details of caching, TTLs, protocol and
>> address selection, etc.  Such a connect() could even support a revised
>> TCP stack which is able to retry with the other addresses at the first
>> subsecond timeout rather than camping on each address in sequence for
>> the typical system default of two minutes.
>
>
> The effect of what you're recommending is to move all of this
> into the kernel, and in the process greatly expand its scope.

Hi Michael,

libc != kernel. I want to move the action into the standard libraries
where it can be done once and done well. A little kernel action on top
to parallelize connection attempts where there are multiple candidate
addresses would be gravy, but not required.

> even if you did this, you'd be saddled with the same problem because
> nothing existing would use an AF_NAME.

It won't instantly fix everything so we shouldn't do it at all?

> what if I want, say, asynchronous
> name resolution? What if I want to use SRV records? What if a new DNS
> RR comes around

Then you do it the long way, same as you do now. But in the 99% of the
time that you're initiating a connection the "normal" way, you don't
have to (badly) reinvent the wheel.

> As far as
> I could tell, standard distos don't have libraries with lower level access to
> DNS (in my case, it needed to not block). Before positing a super-deluxe
> gethostbyxx that does addresses picking, etc, etc it would be better to
> lobby all of the distos to settle on a decomposed resolver library from
> which that and more could be built.

(A) Revised standards are -how- multiple OSes from multiple vendors
coordinate the deployment of an identical capability.

(B) Application programmers generally DO want the abstraction from
"DNS" to "Name resolution." If there's an /etc/hosts name or a NIS
name or a Windows name available, you ordinarily want to use it. You
don't want to build extra code to search each name service
independently any more than you want to build extra code to cycle
through candidate addresses.

Regards,
Bill Herrin

-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
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