dns and software, was Re: Reliable Cloud host ?

Wed Feb 29 21:20:53 UTC 2012

On Wed, Feb 29, 2012 at 4:02 PM, Joe Greco <jgreco at ns.sol.net> wrote:
> In the specific case of TTL, the problem is made much worse due to the
> way most client code has hidden this data from developers, so that many
> developers don't even have any idea that such a thing exists.
>
> I'm not sure how to see that a design failure of the TTL mechanism.

Hi Joe,

You shouldn't see that as a design failure of the TTL mechanism. It
isn't. It's a failure of the system of which DNS TTL is a component.
The TTL component itself was reasonably designed.

The failure is likened to installing a well designed sprinkler system
(the DNS with a TTL) and then shutting off the water valve
(gethostbyname/getaddrinfo).

> I don't see developers ignoring DNS and hardcoding IP addresses into
> code as a failure of the DNS system.

It isn't. It's a failure of the sockets API design which calls on
every application developer to (a) translate the name to a set of
addresses with a mechanism that discards the TTL knowledge and (b)
implement his own glue between name to address mapping and connect by
address.

It would be like telling an app developer: here's the ARP function and
the SEND function. When you Send to an IP address, make sure you
attach the right destination MAC. Of course the app developer gets it
wrong most of the time.

Regards,
Bill Herrin

-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004