andrew at sawdog
Oct 12, 2006, 10:52 AM
Post #22 of 29
(2419 views)
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FYI, there's a problem with your host Justizin:
> server ns1.zoneedit.com
Default server: ns1.zoneedit.com
Address: 207.234.248.200#53
> cvs.zope.org
Server: ns1.zoneedit.com
Address: 207.234.248.200#53
Name: cvs.zope.org
Address: 63.240.213.173
> server ns.qutang.net
Default server: ns.qutang.net
Address: 70.84.6.50#53
> cvs.zope.org
Server: ns.qutang.net
Address: 70.84.6.50#53
Name: cvs.zope.org
Address: 63.240.213.171
>
In my opinion, the registrar should only have zoneedit.com servers in it for
the time being.
Andrew
On 10/12/06 11:02 AM, "Justizin" <justizin [at] siggraph> wrote:
> On 10/12/06, Lennart Regebro <regebro [at] gmail> wrote:
>> Just a couple of notes here.
>>
>> Although zoneedit has been running fine for me for years without a
>> single problem, obviously it would be nice with some backup.
>> Preferably something with another ISP and located on like another
>> continent or something. Two of these backups would be even better.
>>
>> But honestly, compare the likelyhood that all three of these would
>> fail at one time, together with the increasing likelyhood than one
>> server of them is misconfigured and starts disturbing the usage for a
>> minor part of the users, then we will quickly realize that the more
>> backups and failsafes we have the larger the likelyhood that something
>> of this will go wrong.
>
> the worst that happens is that some changes fail to propogate.
> changes to DNS should always be approached with the assumption that
> this will happen. What's worse is for there to be no copy of a zone
> available.
>
> It should never be necessary for an A record to change immediately,
> because this cannot be relied upon. The best defense to this is,
> however, to set TTLs at 300s, or 5 minutes, about a week in advance.
>
>> 8 servers seems to be to be a complete overkill, and it will only
>> cause problems. I will change my mind on this the time all zone-edit
>> servers stop working at the same time as two of the backups fail.
>
> It could cause problems, and that's why we aren't really using eight
> servers right now, but it should not cause problems. It is a
> challenge, also, that our DNS is not hosted in the same location as
> the website. So, it's possible that DNS will be unreachable when an
> outage occurs, i.e. a fibre being cut in the middle of the ocean, and
> this outage may not actually affect our site.
>
> I bet ten bucks if we rely entirely on zoneedit's nameservers that
> this will happen once for at least twelve hours for some significant
> region of the world within the next year.
>
>> Don't overcomplicate things. It just makes them fail.
>
> This assumption really has nothing to do with what happened this week.
>
> What happened this week was either:
>
> (a) a typo
>
> (b) an erroneously truncated string
>
> If there were only two nameservers, they would have pointed at the
> wrong IP, and the site would have been perceptually unavailable for a
> few hours to two days for various people. If there were eight, the
> same would happen, for about the same time frame.
>
> So, if you want to only use two nameservers, that's okay with me.
> Remember to wake me up when the zone is unreachable for someone and we
> want to run more. :)
>
> I always assume, if anything, that some machines, network connections,
> disk drives, etc.. will invariably fail, and that you can never have
> too many if they are available. I like the idea of a group of zope
> community members collectively providing DNS service. Maybe we should
> even talk about running multiple copies of the flat content in
> different places. If my site goes down, esp if one of my machines
> fail, I much prefer to feel comfortable that I can reach zope.org than
> rely on the possibility that i might have copies of recent releases in
> another location. if i'm going to keep copies of the releases around
> for myself, might as well mirror them, eh?
>
> While having a set of servers configured by various people sounds as
> if it would be overcomplicated, with proper planning and coordination,
> we should be able to keep it simple.
>
> When making changes to DNS, always assume that for 48 hours there will
> be between a 90-10 and 10-90 split between people who have your new
> records and people who have old records. When changing nameservers,
> double or triple this, because some people will have cached records
> from the old nameserver *and* more recently cached NS records, so they
> may continue querying the old nameserver until the cached NS record
> itself expires.
>
> When something critical like svn/cvs or the main website need to be
> changed, again, it is necessary to drop the TTL, on the entire zone,
> even, to something really short like 300s about a week in advance.
> This ensures that everyone in the world has a copy of the zone which
> says: "no copy of this zone and no records in this zone are good for
> longer than five minutes.". Just before a switch is made, you can
> proxy the old front-end apache server to the new host explicitly, and
> then update records. for five or ten minutes some people's requests
> will be slow because they are possibly doubling-back across the
> internet, but at least they can't really tell what's going on, just
> that for a few minutes it is a 'little bit slow'.
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