2.7 - Hostname resolution in network-get omits loopback IPs

[manadart]

Description of change

When a manual machine is provisioned using a FQDN, that name is what is returned by the instance-poller for provider addresses. This means that this name is often also returned as the preferred private and public machine addresses.

In turn, when network-get runs for a unit on such a machine, the FQDN is resolved before returning an address result. When it resolves addresses, it returns the first it finds.

We have observed cases where the machine hosts file has an entry like this:

127.0.1.1 hostname.fqdn hostname

This means that the IP returned by network-get is not usable by relations to the unit.

This patch ensures that where possible, we filter 127.*.*.* addresses before returning host-name resolved addresses. If filtering removes all addresses, we log a warning message to give the operator some information for possible resolution.

QA steps

To do this, I have a LXD profile that includes my Juju SSH key in authorised keys for the "ubuntu" user.

• Create 2 LXD machines with the profile. I named them manual-ctrl and manual-m1.
• juju bootstrap manual/ssh:ubuntu@<manual-ctrl IP> net-get-test --debug --no-gui.
• Use lxc exec manual-m1 bash and add an entry to the hosts file like this:
  127.0.1.1 manual-m1.lxd manual-m1.
• Add an entry to /etc/hosts on the host machine:
  <manual-m1 IP> manual-m1.
• juju add-machine ssh:ubuntu@manual-m1.
• juju deploy percona-cluster mysql --to 0 and await quiescence.
• juju run --unit mysql/0 "network-get --format yaml db".
• Result should show the hostname, but not the IP from the container host file:

bind-addresses:
- macaddress: ""
  interfacename: ""
  addresses:
  - hostname: manual-m1
    address: ""
    cidr: ""
...

• juju debug-log --include mysql/0 should include a warning entry like this:

unit-mysql-0: 13:36:00 WARNING worker.uniter.jujuc no usable addresses resolved for host "manual-m1"
        resolved: [127.0.1.1]
        consider editing the hosts file, or changing host resolution order via /etc/nsswitch.conf

Documentation changes

None.

Bug reference

https://bugs.launchpad.net/juju/+bug/1831580

[manadart]

network_get should not return machine-local addresses

[manadart]

!!build!!

[achilleasa]

The last commit LGTM.

Can you also update the bit about filtering in the PR description and add something along the lines of "if only loopback IPs are found, we log an error advising the operator on how to tweak the system settings to ensure proper IP discoverability"?

[manadart]

$$merge$$

[howbazaar]

$$merge$$