On Mon, Nov 30, 2020 at 6:56 AM Stephen Finucane <stephenfin@redhat.com> wrote:
When attaching a port to an instance, nova will check for DNS support in neutron and set a 'dns_name' attribute if found. To populate this attribute, nova uses a sanitised version of the instance name, stored in the instance.hostname attribute. This sanitisation simply strips out any unicode characters and replaces underscores and spaces with dashes, before truncating to 63 characters. It does not currently replace periods and this is the cause of bug 1581977 [1], where an instance name such as 'ubuntu20.04' will fail to schedule since neutron identifies '04' as an invalid TLD.
The question now is what to do to resolve this. There are two obvious paths available to us. The first is to simply catch these invalid hostnames and replace them with an arbitrary hostname of format 'Server-{serverUUID}'. This is what we currently do for purely unicode instance names and is what I've proposed at [2]. The other option is to strip all periods, or rather replace them with hyphens, when sanitizing the instance name. This is more predictable but breaks the ability to use the instance name as a FQDN. Such usage is something I'm told we've never supported, but I'm concerned that there are users out there who are relying on this all the same and I'd like to get a feel for whether this is the case first.
So, the question: does anyone currently rely on this inadvertent "feature"?
I took a look and we (at Verizon Media) have users that create instances with fqdn-like names (VMs and BMs). I didn't look to see how many instances have such names, but we have tens of thousands of instances and eyeballing one of our clusters, > 90% of them have such names. --ruby
Cheers, Stephen
[1] https://launchpad.net/bugs/1581977 [2] https://review.opendev.org/c/openstack/nova/+/764482