config-changed does not regenerate config file

[Alvaro Uria]

* metadata.yaml only supports trusty and xenial
* new v2.24 packages have been added to Thruk ppa.
* Bionic support needs to be tested and charm updated.

[Alvaro Uria (aluria)]

Tested to add bionic "series" in metadata.yaml.

"""
cd thruk-master-charm
juju deploy . thruk-master --series bionic
cd ../thruk-external-agent-charm
juju deploy . thruk-test-external-agent --series bionic
juju add-relation thruk-master thruk-test-external-agent
"""

thruk-test-external-agent uses "url=http://127.0.0.1/" by default, and following "juju config ..." to update "url" value doesn't work as expected:

In thruk-master unit, /var/log/thruk/thruk.log shows:
"""
[2018/11/26 14:54:11][juju-92b911-11][ERROR][Thruk] No Backend available
[2018/11/26 14:54:11][juju-92b911-11][ERROR][Thruk] juju: remote site returned rc: 1 - "authorization failed, no auth key specified for http://127.0.0.1/thruk/cgi-bin/remote.cgi\n" (http://127.0.0.1)
[2018/11/26 14:54:11][juju-92b911-11][ERROR][Thruk] on page: http://10.205.6.183/thruk/cgi-bin/tac.cgi?_=1543244051029
[2018/11/26 14:54:11][juju-92b911-11][ERROR][Thruk] User: thrukadmin
"""

/var/cache/thruk/lmd/lmd.ini had to be manually updated:
"""
[[Connections]]
name = 'juju'
id = '5a105e8b9d40e1329780d62ea2265d8a'
source = ['http://127.0.0.1/']
auth = '' ## <-- needed to be manually updated
"""

Then, "service thruk restart", and lmd.ini got automatically updated to the new data shared via juju relation with thruk-external-agent-charm:
"""
[[Connections]]
name = 'test1'
id = '5a105e8b9d40e1329780d62ea2265d8a'
source = ['http://10.205.6.227/']
auth = '0b0d118151ab45cbefd167d4f0a36b21'
"""

TL;DR: thruk-master-charm may need to be rewritten to reactive charm (now uses the Service framework) to better manage config changes (even coming from relations).

[Alok G Singh (alephnull-b)]

So it turns out that this is not related to bionic support at all.

The root cause for this problem is that the charm thinks that the thruk service service is called thruk-master. It should be called thruk. The charm correctly populates /etc/thruk/thruk_local.conf but since the thruk service is not restarted /var/cache/thruk/lmd/lmd.ini is not updated.

This bug has probably existed since trusty since the playbook for thruk mentions that apache should be reloaded. This in turn reloads thruk and the config is generated correctly.