---
fixes:
  - |
    Nova will now replace periods (``.``) with dashes (``-``) when sanitizing an
    instance's display name for use as a hostname.

    Nova publishes hostnames for instances via the metadata service and config
    drives. This hostname is based on a sanitized version of the instance name
    combined with the domain value specified in ``[api] dhcp_domain``. The
    previous sanitization of the hostname included the replacement of whitespace
    and underscores with dashes and the stripping of unicode characters along
    with leading and trailing periods and dashes. It did not, however, include
    the removal of periods in the name. Periods are not valid in the hostname
    or, more specifically, in the host-specific or leaf label (the ``host`` in
    ``host.example.com``) and their presence can cause conflicts when ``[api]
    dhcp_domain`` is configured, leading to instances being mistakenly
    configured with hostnames like ``host.example.com.example.com``. More
    pressingly, their use can result in a failure to boot instances if DNS
    integration is enabled in neutron, likely via designate, as the hostname is
    identified as a FQDN (fully-qualified domain name) by neutron and reasonable
    instance names like ``test-ubuntu20.04`` will be rejected as invalid FQDNs,
    in this case because the name would yield a TLD (top-level domain) of ``04``
    and TLDs cannot be entire numerical. To avoid these issues, periods are now
    replaced with dashes.
