Re: DNS lookup for git.postgresql.org

On Wed, Jun 30, 2021 at 12:53:24PM -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > On Tue, Jun 29, 2021 at 11:26:54PM -0400, Tom Lane wrote:
> >> My buildfarm animals frequently complain of being unable to contact the
> >> buildfarm server.  Sometimes there's an identifiable problem at my end,
> >> but usually not.  A typical error looks like
> >> error getting branches of interest: 500 Can't connect to buildfarm.postgresql.org:443 (Network is unreachable) at
./run_branches.plline 199.
 
> 
> > OK, thanks.  When no one said they saw similar behavior, I started
> > digging deeper.  It seems on Debian 10, bind/named uses IPv6 by default,
> > and my ISP, Verison FIOS, doesn't support IPv6 yet;  see:
> >     https://www.reddit.com/r/Fios/comments/li4ri7/does_fios_support_ipv6/
> 
> Oh, that's an interesting point.  I have no IPv6 connectivity here either.
> I'd figured out some time ago that with recent bind versions I need to use
> named's "-4" option to prevent DNS lookup timeouts ... but now I see that
> that doesn't stop it from returning IPv6 addresses.  I wonder if the
> failures occur when my animals try to use the buildfarm server's IPv6
> address.  I'll try the hack mentioned in the serverfault thread.

Oh, I used the -4 option and my failures stopped.  Glad this thread was
helpful for you too.  I never expected IPv6 to lead to failures, just
possible delays, but I have now learned, at least with DNS, it can cause
failures too.  I will also add the bind options mentioned to disable
dnssec and aaaa records.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.