Need a consistent means to know the hostname of a machine

[Xav Paice]

Currently various providers list the dns-name, and instance-id, for machines but oftentimes the cloud provider doesn't provide the hostname, so in dns-name we see an IP address and in instance-id we might see an instance uuid. We do have occasions when it's necessary to know the actual hostname of a machine, outside the times we can run code on the unit itself or via ssh.

It would be good to include in machine data a 'hostname' field that is populated by the machine agent, to read whatever is returned by a command like 'hostname', or os.Hostname().

[Xav Paice (xavpaice)]

Example output from an openstack provider machine:

$ juju show-machine 0 --format yaml
model: hacluster
machines:
  "0":
    juju-status:
      current: started
      since: 09 Mar 2021 10:07:25+13:00
      version: 2.9-beta1
    dns-name: 10.5.0.16
    ip-addresses:
    - 10.5.0.16
    - 252.0.16.1
    instance-id: 36364855-396d-436b-90f2-4134d49d58d4
    machine-status:
      current: running
      message: ACTIVE
      since: 09 Mar 2021 10:06:34+13:00
    modification-status:
      current: idle
      since: 09 Mar 2021 10:05:47+13:00
    series: xenial
    network-interfaces:
      ens3:
        ip-addresses:
        - 10.5.0.16
        mac-address: fa:16:3e:cd:4c:af
        gateway: 10.5.0.1
        space: alpha
        is-up: true
      fan-252:
        ip-addresses:
        - 252.0.16.1
        mac-address: 06:b8:17:f1:57:98
        space: alpha
        is-up: true
    hardware: arch=amd64 cores=1 mem=2048M root-disk=20480M availability-zone=nova

Compared to Maas output:
machines:
  "60":
    juju-status:
      current: started
      since: 02 Feb 2021 21:11:48Z
      version: 2.8.7
    dns-name: 1.2.3.4
    ip-addresses:
    - 1.2.3.4
    - 192.168.1.2
    instance-id: whpchd
    display-name: host1
    machine-status:
      current: running
      message: Deployed
      since: 24 Dec 2020 20:36:51Z
    modification-status:
      current: idle
      since: 24 Dec 2020 20:24:19Z
    series: xenial
    network-interfaces:
      bond0.120:
        ip-addresses:
        - 192.168.1.2
        mac-address: e4:43:4b:f6:58:f8
        space: space-2
        is-up: true
      eno3:
        ip-addresses:
        - 1.2.3.4
        mac-address: e4:43:4b:f6:58:fc
        gateway: 1.2.3.1
        space: space-0
        is-up: true
    constraints: tags=compute
    hardware: arch=amd64 cores=104 mem=589824M tags=294254-compute availability-zone=default

[Achilleas Anagnostopoulos (achilleasa)]

PR https://github.com/juju/juju/pull/12754 includes a fix for 2.8