[Bug 1826419] Re: dhcp agent configured with mismatching domain and host entries

[OpenStack Infra]

Fix proposed to branch: master
Review: https://review.opendev.org/657806

** Changed in: neutron
       Status: New => In Progress

** Changed in: neutron
     Assignee: Miguel Lavalle (minsel) => James Page (james-page)

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https://bugs.launchpad.net/bugs/1826419

Title:
  dhcp agent configured with mismatching domain and host entries

Status in neutron:
  In Progress
Status in neutron package in Ubuntu:
  New

Bug description:
  Related bug 1774710 and bug 1580588

  The neutron-dhcp-agent in OpenStack >= Queens makes use of the
  dns_domain value set on a network to configure the '--domain'
  parameter of the dnsmasq instance that supports it;  at the same time,
  neutron makes use of CONF.dns_domain when creating dns_assignments for
  ports - this results in a hosts file for the dnsmasq instance which
  uses CONF.dns_domain and a --domain parameter of network.dns_domain
  which do not match.

  This results in a search path on instances booted attached to the
  network which is inconsistent with the internal DNS entries that
  dnsmasq responds with:

    root at bionic-045546-2:~# host 192.168.21.222
    222.21.168.192.in-addr.arpa domain name pointer bionic-045546-2.jamespage.internal.
    root at bionic-045546-2:~# host bionic-045546-2
    bionic-045546-2.designate.local has address 192.168.21.222

  In the above example:

    CONF.dns_domain = jamespage.internal.
    network.dns_domain = designate.local.

  Based on previous discussion in bug 1580588 I think that the
  dns_domain value for a network was intented for use for external DNS
  integration such as that provided by Designate.

  The changed made under commit:

    https://opendev.org/openstack/neutron/commit/137a6d61053

  appear to break this assumption, producing somewhat inconsistent
  behaviour in the dnsmasq instance for the network.

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