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

[Trevor Cordes]

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.