[stable/prometheus-operator] allow empty ruleSelector and ruleNamespa…

[ghost]

…ceSelector

Currently an empty ruleSelector or ruleNamespaceSelector does not select
all PrometheusRules or Namespaces respectively. Fix the prometheus
template to allow empty ruleSelector and ruleNamespaceSelector.

What this PR does / why we need it:

Currently an empty ruleSelector or ruleNamespaceSelector does not select
all PrometheusRules or Namespaces respectively. Fix the prometheus
template to allow empty ruleSelector and ruleNamespaceSelector.

Special notes for your reviewer:

@gianrubio By default all ServiceMonitors and PrometheusRules in all namespaces will be selected.

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md

[ghost]

/assign @gianrubio

[vsliouniaev]

@ntroast The guidelines specify that charts should select their own resources by default, and from what you are saying this chart breaks this requirement : https://github.com/helm/charts/blob/master/REVIEW_GUIDELINES.md#deployments-statefulsets-daemonsets-selectors

[ghost]

@vsliouniaev Sorry, I should have been more clear. By default ruleSelectorNilUsesHelmValues and serviceMonitorSelectorNilUsesHelmValues are true. This will add a selector to select based on labels just like before. When these values are false then all will be selected in all namespaces. Therefore, this meets the selectors requirement.

[gianrubio]

/ok-to-test
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[vsliouniaev]

Your changes to the description of the behaviour of the namespace selector don't correspond to what is described in the API for prometheus operator. https://github.com/coreos/prometheus-operator/blob/master/Documentation/api.md#namespaceselector

Also, pretty certain that the behaviour of nil and {} is equivalent and cannot be distinguished by Helm templating