Change 221148 had a related patch set uploaded (by Glaisher):
Redirect wikipedia.is to is.wikipedia.org

https://gerrit.wikimedia.org/r/221148

@Slaporte It looks to me like DNS itself is actually fine, it points to our servers. Just that the webserver didn't have any config for it. So it showed:

Domain not configured

This domain points to a Wikimedia Foundation server, but is not configured on this server.

at http://wikipedia.is/

Glaisher uploaded a change to fix that, but it doesn't seem to match the description of "faulty DNS setup".
Could you paste more details from their mail?

Change 221148 merged by Dzahn:
Redirect wikipedia.is to is.wikipedia.org

https://gerrit.wikimedia.org/r/221148

Hi @Dzahn, this is what I got from the registrar:

The following errors are registered when ISNIC attempts to check the zone for domain wikipedia.is:

Test results for "NS0.WIKIMEDIA.ORG":
The serial number is not in sync with the primary nameserver
Test results for "NS2.WIKIMEDIA.ORG":
The serial number is not in sync with the primary nameserver

@Glaisher: We ran into a very strange bug when trying to add that seeminly easy redirect. see below

https://gerrit.wikimedia.org/r/#/c/221282/
https://gerrit.wikimedia.org/r/#/c/221291/

@Slaporte Ok, that would be unrelated to the missing Apache redirect. We'll get into that seperately.

In T103915#1406090, @Slaporte wrote:

Hi @Dzahn, this is what I got from the registrar:

The following errors are registered when ISNIC attempts to check the zone for domain wikipedia.is:

Test results for "NS0.WIKIMEDIA.ORG":
The serial number is not in sync with the primary nameserver
Test results for "NS2.WIKIMEDIA.ORG":
The serial number is not in sync with the primary nameserver

Currently, I can confirm no such problem exists (and I didn't do anything to fix it). All 3x of our nameservers report identical SOA's, including the serial. Here's the raw dig output, as well as a double-check with md5 hashing to ensure there's no obscure typo that's hard for humans to notice:

bblack-mba:~ bblack$ for x in 0 1 2; do dig +short @ns$x.wikimedia.org wikipedia.is SOA; done
ns0.wikimedia.org. hostmaster.wikimedia.org. 2015061022 43200 7200 1209600 3600
ns0.wikimedia.org. hostmaster.wikimedia.org. 2015061022 43200 7200 1209600 3600
ns0.wikimedia.org. hostmaster.wikimedia.org. 2015061022 43200 7200 1209600 3600
bblack-mba:~ bblack$ for x in 0 1 2; do dig +short @ns$x.wikimedia.org wikipedia.is SOA|md5; done
730520d5fee01dde09ba1144a71f75d1
730520d5fee01dde09ba1144a71f75d1
730520d5fee01dde09ba1144a71f75d1

Their checking of this, if it's an automated check on a periodic basis, seems non-sensical to me in the first place. As changes are rolled out to nameservers, serial numbers get updated, and there is never perfect sync between the multiple nameservers for a domainname. Most of the time SOA serials would be in sync, but there will always be race-conditions where the serials are temporarily out of sync during updates. If it's just a one-time check when first registering, I guess it's not bad as a sanity measure, but still they must have just had really bad timing when checking it...

Change 221877 had a related patch set uploaded (by Glaisher):
Redirect wikipedia.is to is.wikipedia.org

https://gerrit.wikimedia.org/r/221877

Change 221877 merged by Dzahn:
Redirect wikipedia.is to is.wikipedia.org

https://gerrit.wikimedia.org/r/221877

the redirects work now, merged and deployed.

[terbium:~] $ apache-fast-test iswiki.urls mw1033
testing 4 urls on 1 servers, totalling 4 requests
spawning threads..

http://wikipedia.is
 * 301 Moved Permanently http://is.wikipedia.org/
http://wikipedia.is/wiki/
 * 301 Moved Permanently http://is.wikipedia.org/wiki/
http://www.wikipedia.is
 * 301 Moved Permanently http://is.wikipedia.org/
https://wikipedia.is
 * 301 Moved Permanently https://is.wikipedia.org/

Can we close this now? @Slaporte Can you ask for reconfirmation from them?

The registrar confirmed that this is resolved. Thanks!