chore(helm): Add comments, clarifying ruler setup

[eranikid]

What this PR does / why we need it:

This PR addresses issue #13027 by adding clarifying comments to the Helm chart's values.yaml.

Problem

When using the Helm chart, if a user defines rules via .Values.ruler.directories,

loki/production/helm/loki/values.yaml

Lines 3104 to 3120 in cc10685

	directories: {}
	# tenant_foo:
	# rules1.txt: |
	# groups:
	# - name: should_fire
	# rules:
	# - alert: HighPercentageError
	# expr: |
	# sum(rate({app="foo", env="production"} |= "error" [5m])) by (job)
	# /
	# sum(rate({app="foo", env="production"}[5m])) by (job)
	# > 0.05
	# for: 10m
	# labels:
	# severity: warning
	# annotations:
	# summary: High error rate

the chart correctly creates ConfigMaps

loki/production/helm/loki/templates/ruler/configmap-ruler.yaml

Line 3 in cc10685

{{- range $dir, $files := .Values.ruler.directories }}

and mounts them

loki/production/helm/loki/templates/ruler/statefulset-ruler.yaml

Lines 112 to 115 in cc10685

	{{- range $dir, $_ := .Values.ruler.directories }}
	- name: {{ include "loki.rulerRulesDirName" $dir }}
	mountPath: /etc/loki/rules/{{ $dir }}
	{{- end }}

to the ruler's filesystem at /etc/loki/rules.

However, if .Values.loki.storage.type is set to a cloud storage provider (e.g., s3, gcs), the ruler is also implicitly configured

loki/production/helm/loki/templates/_helpers.tpl

Lines 322 to 329 in cc10685

	{{- define "loki.rulerStorageConfig" -}}
	{{- if .Values.minio.enabled -}}
	type: "s3"
	s3:
	bucketnames: ruler
	{{- else if eq .Values.loki.storage.type "s3" -}}
	{{- with .Values.loki.storage.s3 }}
	type: "s3"

to use that same provider for its rule storage. This causes the ruler to ignore the local rules mounted from the ConfigMaps, as it's looking for them in the cloud backend instead of the local filesystem.

---

Workaround

To resolve this, the user must manually override the ruler's storage configuration to point to the local directory:

ruler:
  config:
    storage:
      # This override is necessary for the ruler to read rules
      # defined in .Values.ruler.directories.
      type: local
      local:
        directory: /etc/loki/rules

This solution is not intuitive and is fragile because it requires the user to hardcode the /etc/loki/rules path, which is an internal implementation detail of the chart.

---

Proposed Solution

While modifying the chart's templates to automatically configure local storage for the ruler, I deemed it was potentially too intrusive and a possible breaking change.

Instead, this PR adds detailed comments to the values.yaml file. These comments explain the behavior and provide the required configuration override, improving the user experience by preventing this common pitfall without introducing breaking changes.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[CLAassistant]

All committers have signed the CLA.

[jkroepke]

As I know, this is not possible unless #18510 is merged.