Comment 8 for bug 1892044

Reviewed: https://review.opendev.org/762112
Committed: https://git.openstack.org/cgit/openstack/oslo.config/commit/?id=9b1ccea642f0769cb6c49bf814ddab62ca5d8180
Submitter: Zuul
Branch: stable/train

commit 9b1ccea642f0769cb6c49bf814ddab62ca5d8180
Author: Hervé Beraud <email address hidden>
Date: Tue Aug 18 15:30:04 2020 +0200

    Add a new type HostDomain.

    HostDomain is like HostAddress with the support of
    _ character - RFC1033

    openstack services are failing to start when a hostname with underscore
    _ is provided.

    Example:

    ```
    overcloud-novacompute_edge1-0.internalapi.localdomain
    overcloud-novacompute_edge1-0.internalapi
    ```

    Nova use `HostAddressOpt` to define `live_migration_inbound_addr`,
    and if a hostname with underscore is present in the config file
    then the service fail to start.

    Example:

    ```
    /etc/nova/nova.conf
    live_migration_inbound_addr =
    overcloud-novacompute_edge1-0.internalapi.localdomain
    ```

    FQDN is a domain name that specifies its exact
    location in the tree hierarchy of the Domain Name System (DNS).

    Underscore are allowed by RFC1033 [1][2][3]. Indeed, while a hostname may not
    contain other characters, such as the underscore character (_), other
    DNS names may contain the underscore.[1][2].
    Systems such as DomainKeys and service records use the underscore.

    These changes allow us to use underscore with the `HostDomain`.

    [1] https://www.ietf.org/rfc/rfc1912.txt
    [2] https://www.ietf.org/rfc/rfc1033.txt
    [3] http://domainkeys.sourceforge.net/underscore.html

    Co-authored-by: Daniel Bengtsson <email address hidden>
    Change-Id: I0a0670207f96a987996d329e5efa9a5eb2ce000c
    Closes-Bug: #1892044
    (cherry picked from commit 6480356928c9ae6169ea1e5a5b5f1df3d6e0dc75)
    (cherry picked from commit f37bcc779347c9e0d1e37258a6d072b718edf7f7)
    (cherry picked from commit 1fcb3e8acd3c229c74c87d80fd183cfc2432bace)