[Labs-l] Reverse DNS for labs public IPs now working

[Alex Monk]

Hi all,

Today my changes to get PTR records for labs public IPs went live. Here are
the details relevant to labs project admins (probably not users so much,
and most likely not people who are just users of tools for example):

For starters, every A record you have pointing to a labs public IP (
208.80.155.128/25) will now be picked up by my script and have a reverse
entry created. For example:

alex at alex-laptop:~$ host beta.wmflabs.org
beta.wmflabs.org has address 208.80.155.135
alex at alex-laptop:~$ host 208.80.155.135
135.155.80.208.in-addr.arpa is an alias for
135.128-25.155.80.208.in-addr.arpa.
135.128-25.155.80.208.in-addr.arpa domain name pointer beta.wmflabs.org.
135.128-25.155.80.208.in-addr.arpa domain name pointer
instance-deployment-cache-text04.deployment-prep.wmflabs.org.

(the 128-25 thing is RFC2317-style delegation, as labs only gets
208.80.155.128-208.80.155.255, not the whole of 208.80.155.*, and therefore
can't have the entirety of 155.80.208.in-addr.arpa. delegated to its
nameservers by Wikimedia production)

The second thing you'll notice above is the extra instance-$instance.$
project.wmflabs.org entry there. This is primarily for cases where you have
an instance with a public IP but no domain pointing at it, and is helpful
to determine what instance is handling requests to an IP anyway.
The instance- records are available to all projects which have control of
their $project.wmflabs.org domain (about 76% of labs projects) - projects
without that may see the instance- records in PTRs but they will not
resolve. Details are available at https://phabricator.wikimedia.org/T104521

The third and final thing is that instances connecting out onto the
internet but which do not have public IPs are seen as 208.80.155.255 - I've
named this internal-server-nat.wmflabs.org.

Alex Monk
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