network-get returns wrong ip for cluster_address when rendering the etcd.conf template

[Andrew Scribner]

In some cases where a node has a mix of ipv4 and ipv6 addresses, etcd may pull the wrong one. This shows in `juju status` as:

```
etcd 3.4.5 active 1 etcd charmstore stable 607 ubuntu Errored with 0 known peers
```

with:
```
$ juju debug-log -i etcd/0 --replay
unit-etcd-0: 14:34:16 WARNING unit.etcd/0.update-status Error: client: etcd cluster is unavailable or misconfigured; error #0: dial tcp 127.0.0.1:4001: connect: connection refused
unit-etcd-0: 14:34:16 WARNING unit.etcd/0.update-status ; error #1: dial tcp 127.0.0.1:2379: connect: connection refused
unit-etcd-0: 14:34:16 WARNING unit.etcd/0.update-status
unit-etcd-0: 14:34:16 WARNING unit.etcd/0.update-status error #0: dial tcp 127.0.0.1:4001: connect: connection refused
unit-etcd-0: 14:34:16 WARNING unit.etcd/0.update-status error #1: dial tcp 127.0.0.1:2379: connect: connection refused
unit-etcd-0: 14:34:16 WARNING unit.etcd/0.update-status
unit-etcd-0: 14:34:16 ERROR unit.etcd/0.juju-log ['/snap/bin/etcd.etcdctl', 'cluster-health']
unit-etcd-0: 14:34:16 ERROR unit.etcd/0.juju-log {'ETCDCTL_API': '2', 'ETCDCTL_CA_FILE': '/var/snap/etcd/common/ca.crt', 'ETCDCTL_CERT_FILE': '/var/snap/etcd/common/server.crt', 'ETCDCTL_KEY_FILE': '/var/snap/etcd/common/server.key'}
unit-etcd-0: 14:34:16 ERROR unit.etcd/0.juju-log b'cluster may be unhealthy: failed to list members\n'
unit-etcd-0: 14:34:16 ERROR unit.etcd/0.juju-log None
unit-etcd-0: 14:34:16 WARNING unit.etcd/0.juju-log Notice: Unit failed cluster-health check
unit-etcd-0: 14:34:17 WARNING unit.etcd/0.update-status Error: client: etcd cluster is unavailable or misconfigured; error #0: dial tcp 127.0.0.1:2379: connect: connection refused
unit-etcd-0: 14:34:17 WARNING unit.etcd/0.update-status ; error #1: dial tcp 127.0.0.1:4001: connect: connection refused
unit-etcd-0: 14:34:17 WARNING unit.etcd/0.update-status
unit-etcd-0: 14:34:17 WARNING unit.etcd/0.update-status error #0: dial tcp 127.0.0.1:2379: connect: connection refused
unit-etcd-0: 14:34:17 WARNING unit.etcd/0.update-status error #1: dial tcp 127.0.0.1:4001: connect: connection refused
unit-etcd-0: 14:34:17 WARNING unit.etcd/0.update-status
unit-etcd-0: 14:34:17 ERROR unit.etcd/0.juju-log ['/snap/bin/etcd.etcdctl', 'member', 'list']
unit-etcd-0: 14:34:17 ERROR unit.etcd/0.juju-log {'ETCDCTL_API': '2', 'ETCDCTL_CA_FILE': '/var/snap/etcd/common/ca.crt', 'ETCDCTL_CERT_FILE': '/var/snap/etcd/common/server.crt', 'ETCDCTL_KEY_FILE': '/var/snap/etcd/common/server.key'}
unit-etcd-0: 14:34:17 ERROR unit.etcd/0.juju-log b''
unit-etcd-0: 14:34:17 ERROR unit.etcd/0.juju-log None
```

and (from the unit)

```
$ journalctl -u snap.etcd.etcd.service
Oct 13 18:39:42 frank-moose systemd[1]: snap.etcd.etcd.service: Failed with result 'exit-code'.
Oct 13 18:39:52 frank-moose systemd[1]: snap.etcd.etcd.service: Scheduled restart job, restart counter is at 1023.
Oct 13 18:39:52 frank-moose systemd[1]: Stopped Service for snap application etcd.etcd.
Oct 13 18:39:52 frank-moose systemd[1]: Started Service for snap application etcd.etcd.
Oct 13 18:39:52 frank-moose etcd.etcd[93173]: Running as system with data in /var/snap/etcd/230
Oct 13 18:39:52 frank-moose etcd.etcd[93173]: Configuration from /var/snap/etcd/common/etcd.conf.yml
Oct 13 18:39:52 frank-moose etcd.etcd[93173]: unexpected error setting up initial-advertise-peer-urls: URL address does not have the form "host:port": https://2607:fea8:c3a1:8f00:216:3eff>
Oct 13 18:39:52 frank-moose systemd[1]: snap.etcd.etcd.service: Main process exited, code=exited, status=1/FAILURE
Oct 13 18:39:52 frank-moose systemd[1]: snap.etcd.etcd.service: Failed with result 'exit-code'.
```

where we see an ipv6 address being used. This is pulled from the top of ingress-addresses
```
$ juju run --unit etcd/0 'network-get cluster'
bind-addresses:
- mac-address: 00:16:3e:02:69:96
  interface-name: eth2
  addresses:
  - hostname: ""
    address: 2607:fea8:c3a1:8f00:216:3eff:fe02:6996
    cidr: 2607:fea8:c3a1:8f00::/64
  - hostname: ""
    address: 2607:fea8:c3a1:8f00::fc1d
    cidr: 2607:fea8:c3a1:8f00::fc1d/128
  - hostname: ""
    address: 10.0.0.42
    cidr: 10.0.0.0/24
  macaddress: 00:16:3e:02:69:96
  interfacename: eth2
egress-subnets:
- 2607:fea8:c3a1:8f00:216:3eff:fe02:6996/128
ingress-addresses:
- 2607:fea8:c3a1:8f00:216:3eff:fe02:6996
- 2607:fea8:c3a1:8f00::fc1d
- 10.0.0.42
```

where [this](https://github.com/charmed-kubernetes/layer-etcd/blob/master/lib/etcd_lib.py#L21) line pulls all addresses and [this](https://github.com/charmed-kubernetes/layer-etcd/blob/master/lib/etcd_lib.py#L29) line uses only the first one (which in this case was ipv6).

[Andrew Scribner (ca-scribner)]

As a quick fix, changing all entries of the ipv6 addresses in /var/snap/etcd/common/etcd.conf.yml to the correct ipv4 address for etcd up and running with a healthy peer.

[George Kraft (cynerva)]

Thanks. Marking this as a duplicate of https://bugs.launchpad.net/charm-etcd/+bug/1913348