Installing influxdb using: `juju deploy influxdb` fails on apt hook. Influxdata repository cannot be verified because of bad gpg key.
Logs:
```
unit-influxdb-6: 15:17:17 ERROR unit.influxdb/6.juju-log Hook error:
Traceback (most recent call last):
File "/var/lib/juju/agents/unit-influxdb-6/.venv/lib/python3.8/site-packages/charms/reactive/__init__.py", line 74, in main
bus.dispatch(restricted=restricted_mode)
File "/var/lib/juju/agents/unit-influxdb-6/.venv/lib/python3.8/site-packages/charms/reactive/bus.py", line 390, in dispatch
_invoke(other_handlers)
File "/var/lib/juju/agents/unit-influxdb-6/.venv/lib/python3.8/site-packages/charms/reactive/bus.py", line 359, in _invoke
handler.invoke()
File "/var/lib/juju/agents/unit-influxdb-6/.venv/lib/python3.8/site-packages/charms/reactive/bus.py", line 181, in invoke
self._action(*args)
File "/var/lib/juju/agents/unit-influxdb-6/charm/reactive/apt.py", line 41, in update
charms.apt.update()
File "/var/lib/juju/agents/unit-influxdb-6/charm/lib/charms/apt.py", line 105, in update
fetch.apt_update(fatal=True) # Friends don't let friends set fatal=False
File "/var/lib/juju/agents/unit-influxdb-6/.venv/lib/python3.8/site-packages/charmhelpers/fetch/ubuntu.py", line 401, in apt_update
_run_apt_command(cmd, fatal)
File "/var/lib/juju/agents/unit-influxdb-6/.venv/lib/python3.8/site-packages/charmhelpers/fetch/ubuntu.py", line 952, in _run_apt_command
_run_with_retries(
File "/var/lib/juju/agents/unit-influxdb-6/.venv/lib/python3.8/site-packages/charmhelpers/fetch/ubuntu.py", line 929, in _run_with_retries
result = subprocess.check_call(cmd, env=env, **kwargs)
File "/usr/lib/python3.8/subprocess.py", line 364, in check_call
raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['apt-get', 'update']' returned non-zero exit status 100.
unit-influxdb-6: 15:17:17 ERROR juju.worker.uniter.operation hook "install" (via explicit, bespoke hook script) failed: exit status 1
unit-influxdb-6: 15:17:17 INFO juju.worker.uniter awaiting error resolution for "install" hook
unit-influxdb-6: 15:17:27 INFO juju.worker.uniter awaiting error resolution for "install" hook
unit-influxdb-6: 15:17:27 INFO unit.influxdb/6.juju-log Reactive main running for hook install
unit-influxdb-6: 15:17:28 INFO unit.influxdb/6.juju-log Initializing Apt Layer
unit-influxdb-6: 15:17:35 WARNING unit.influxdb/6.install W: GPG error: https://repos.influxdata.com/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D8FF8E1F7DF8B07E
unit-influxdb-6: 15:17:35 WARNING unit.influxdb/6.install E: The repository 'https://repos.influxdata.com/ubuntu xenial InRelease' is not signed.
unit-influxdb-6: 15:17:35 INFO unit.influxdb/6.juju-log Failed executing 'add-apt-repository --yes deb https://repos.influxdata.com/ubuntu xenial stable'. Will retry in 10 seconds
unit-influxdb-6: 15:17:45 INFO unit.influxdb/6.juju-log Invoking reactive handler: reactive/apt.py:39:update
unit-influxdb-6: 15:17:45 INFO unit.influxdb/6.juju-log status-set: maintenance: Updating apt cache
unit-kapacitor-2: 15:17:48 INFO unit.kapacitor/2.juju-log Reactive main running for hook update-status
unit-kapacitor-2: 15:17:48 INFO juju.worker.uniter.operation ran "update-status" hook (via explicit, bespoke hook script)
unit-influxdb-6: 15:17:49 WARNING unit.influxdb/6.install W: GPG error: https://repos.influxdata.com/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D8FF8E1F7DF8B07E
unit-influxdb-6: 15:17:49 WARNING unit.influxdb/6.install E: The repository 'https://repos.influxdata.com/ubuntu xenial InRelease' is not signed.
....
```
Influxdata is referencing an other gpg key for installing legacy influxdb: https://docs.influxdata.com/influxdb/v1.8/introduction/install/
Current workaround:
```
INFLUXDB_PGP=$(curl -s https://repos.influxdata.com/influxdata-archive_compat.key)
juju deploy influxdb --config install_keys="$INFLUXDB_PGP"
```
Following their documentation, the fix could:
- using the Archive Compat gpg key as default `install_keys` value
- using `deb https://repos.influxdata.com/ubuntu stable main` as default `install_sources` value
This has been fixed in revision 27 (in the stable channel).