[mdlug] Server maintenance

[Jay Nugent]

Greetings,

On Sat, 17 Nov 2012, Carl T. Miller wrote:

> On 11/17/2012 11:45 AM, Adam Tauno Williams wrote:
>>  I think people generally use "propagate" to indicate the amount of time it
>>  takes for clients to realize the change. And I generally double the
>>  expected time when telling anyone else how long it will take.
>
> Yes, and propagate means to have offspring or to be something
> tangible that grows or moves.  DNS records don't do either of
> those things.  Promulgate is the word for the spread of the
> awareness of an intangible item, such as a law or a DNS record.

    Since DNS is an "on demand" system, NOTHING moves unless someone 
actually makes a querry.  If the TTL has expired, the requesting server 
performs a recursive lookup to the authoratative server and then caches 
the result.  It makes NO further attempts to get 'newer' data until the 
TTL has expired *AND* a user of that server requests a resolve.

    But my point was:  GOOD engineering is to always reduce the TTL on the 
AUTHORATATIVE server to a low TTL.  Then WAIT for the old TTL time to 
expire BEFORE performing the desired server move.  Failing to follow this 
practice and then BLAME the Internet (or others) is just plain wrong and a 
cop out.

    I have helped many ISP's and businesses move critical servers to new 
networks with ZERO down time. And have watched others NOT follow these 
simple rules and suffer many DAYS of down time.  Borders Books once moved 
an online order system from one web hosting company to another just a few 
weeks before Christmas.  They had a 5 DAY TTL and then claimed that the 
"Internet needed to propogate the new settings" and took no responsibility 
for their bad engineering.  WTF!!!  That company simply deserved to 
die....

    DNS hosting services that do not allow the owner of a namespace to 
manage their resource records (RR), including their SOA record, are just 
crap!  Find a professional DNS hosting service who can do things right.


> Incidentally, the reason so many places say it takes 24 hours to
> promulgate is that Windows has a local cache where it keeps
> records for 24 hours regardless of the ttl of the record.

  Microsoft and Comcast who modify TTL caches times are just wrong and
should be avoided at all costs.  It is none of their business what people
set their TTL times to and they should NOT change them.  If they figure 
that recursive lookups are too much load on their servers, then they need 
to either provide adaquate servers/bandwidth or get the out of the 
business.


     --- Jay

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