[RndTbl] programatically determine if DNS is down or blocked?

Theodore Baschak theodore at ciscodude.net
Fri Apr 8 10:47:13 CDT 2016

On Thu, Apr 7, 2016 at 11:49 PM, Trevor Cordes <trevor at tecnopolis.ca> wrote:

> On 2016-04-07 Adam Thompson wrote:
> > Trevor, why don't you just pay $5/month for a VPS somewhere out on
> > the 'net (in Canada, even!) with static IP addresses and use that as
> > your central coordination point?  If it's still just the principle of
> > the thing, well, keep flogging away at it.
> This isn't that thing (and any other "things" I may have had are
> already on static IP).  The issue here is the mitigation of a problem I
> had a couple of months ago where a Major US Hosting Provider I have an
> app on decided to block my DNS. App went completely mental and crashed
> nearly everything.
> Investigating the code paths it is very clear I need to do some
> delicate things with the results of DNS queries.  To do this reliably I
> need to know that DNS is working.  That means if Hosting Provider
> blocks me, I want to stop doing delicate things.  If my own named dies
> (now that I don't rely on said hosting provider's DNS server), I want to
> stop doing delicate things.
> It's funny, but not much discussion of this out on the net... I guess
> no one else needs a reliable way to tell if DNS is "working".  And if
> they do, they're coming up with proprietary solutions (as I am, it
> seems).  Granted, the app in question is doing some stuff that not many
> others are doing...
> I have some good ideas now, mostly just an aggregation of a bunch of
> mini tests I can run whenever a lookup fails.  Then, if the tests fail
> (i.e. DNS is "down") I can just "pause" my app until situation is
> resolved. Add in some time-caching so as to not waste too many cycles
> on this, and voila, I should be able to better survive any of myriad
> possible DNS issues... In theory. I didn't want to code it myself, but
> looks like I'll have to.

Have you looked at running multiple recursive resolvers on your system and
using a load balancer to always hit a live one?

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