2.0 beta 14 + openstack: generated hostnames exceed 255 byte limit

[James Page]

I'm using juju 2.0 beta 14 with the openstack provider; the hostnames generated for instances are quite long, which when combined with the domain (openstacklocal), push the total hostname over the limit that most OS's can deal with:

  juju-fd943864-df2e-4da1-8e7d-5116a87d4e7c-machine-14.openstacklocal

In my context (testing OpenStack ontop of OpenStack), this causes live-migration to fail as qemu attempts to parse the hostname string, but will only read the first 63 characters (the example above is 67).

The 'juju-fd943864-df2e-4da1-8e7d-5116a87d4e7c-machine-14' should be more efficient in its use of the total permitted length.

Reference:

http://stackoverflow.com/questions/8724954/what-is-the-maximum-number-of-characters-for-a-host-name-in-unix

[Ryan Beisner (1chb1n)]

Please be aware that this is a 2.0 adoption blocker for OpenStack CI to go all-in with Juju 2, as we do the majority of our charm testing on top of OpenStack using Juju.

[Ryan Beisner (1chb1n)]

With "juju-fd943864-df2e-4da1-8e7d-5116a87d4e7c-machine-14" being 53 characters, that doesn't give enterprises much to work with for FQDNs including their domain name: 10 characters aiui.

[Ryan Beisner (1chb1n)]

Reference: https://www.ietf.org/rfc/rfc1035.txt

and

http://manpages.ubuntu.com/manpages/xenial/man2/gethostname.2.html

[Andrew Wilkins (axwalk)]

I've got a change that I'll propose soon that names the instances like:

    juju-<uuid-suffix>-<model-name>-N

where uuid-suffix is the last 6 characters of the model UUID.

e.g. juju-df7591-controller-0.

The model name is really there just for informational purposes, so an operator can tell at a glance what model the instance belongs to. If it's more useful to have super short names, we could remove that.