Support configure alertmanager

[clyang82]

Allow to configured alertmanager in ruler and then enabling me to easily forward alerts from alertmanager:

1. expose alertmanagersURL to be able to configure alertmanager url
2. expose rulesConfig to be able to configure name and key

• name: rule configmap name
• key: rule file name

/assign @squat

[squat]

This assumes that the key used in the configmap ends in rules.yaml, which is mysterious because it is not communicated to the user. Can we instead use the pattern of requiring a rulesFileKey in the jsonnet config and use that name instead?

[clyang82]

Great comments. Thanks @squat I would like to just use *.yaml instead, because the configmap may contain multiple files. Is that OK?

[squat]

The trouble is that there is no guarantee that the configmap key will even end in .yaml. The user could write a configmap where the keys are

foo: ...
bar: ...
rules: ...

each of these keys could have a valid rules file for the value, but the keys don't end in .yaml and thus this flag wouldn't work. File extensions are helpful hints and conventions but are not required.
Similarly, what if the configmap hold multiple keys that end in .yaml but only ONE of them is actually a rules file? Then the ruler would be attempting to read something it can't understand, potentially causing problems.

[squat]

we need to be consistent here; it should either be rulesConfigMapName or ruleConfigMapName without the s

[clyang82]

forgot to update the message.

[squat]

lgtm from my side

Cc @metalmatze

[metalmatze]

Definitely a really good change and addition 👍
I wonder as to why we need this in the mixin for alertmanagers?

                ] + [
                  '--rule-file=/etc/thanos/rules/' + tr.config.ruleFileKey,
                ],
                volumeMounts+: [
                  { name: 'rules-config', mountPath: '/etc/thanos/rules' },
                ],

[metalmatze]

Perfect! 👍