[Bug 1538812] Re: Relies on DNS to resolve own hostname

[James Page]

AFAICT this code has not changed in quite some time; so I'm not sure
what's causing the change in behaviour that you are seeing.

Which provider are you using?  It would be helpful to understand so we
can see the full context.

Having a final attempt using gethostbyname might be a sensible
improvement - from memory this might return 127.0.1.1 on quite a few of
the Juju providers, but that's worth testing with to see.

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https://bugs.launchpad.net/bugs/1538812

Title:
  Relies on DNS to resolve own hostname

Status in ceph package in Juju Charms Collection:
  New
Status in cinder package in Juju Charms Collection:
  New
Status in nova-compute package in Juju Charms Collection:
  New

Bug description:
  In charm/hooks/utils.py, the get_host_ip method seems to rely on DNS
  to resolve host names:

  @cached
  def get_host_ip(hostname=None):
      if config('prefer-ipv6'):
          return get_ipv6_addr()[0]

      hostname = hostname or unit_get('private-address')
      try:
          # Test to see if already an IPv4 address
          socket.inet_aton(hostname)
          return hostname
      except socket.error:
          # This may throw an NXDOMAIN exception; in which case
          # things are badly broken so just let it kill the hook
          answers = dns.resolver.query(hostname, 'A')
          if answers:
              return answers[0].address

  Firstly, the dns.resolver.query call strikes me as incredibly silly.
  What if the other node in not resolvable via DNS, but its name is in
  /etc/hosts? What if the other node *is* in DNS, but is a CNAME? And,
  bottom line, why not simply use socket.gethostbyname() here?

  Secondly, this currently (as of today) breaks a Ceph deployment. It
  definitely didn't do so a month ago, so whatever it was that changed
  in the interim, this is a regression. I don't know if this code path
  wasn't there earlier, or whether it was just never hit. But it
  definitely used to work, and no longer does.

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