[collector] failing to add additional groups in prometheus rules

[kkantonop]

I'm trying to add an additional custom rule on top of the default rules in prometheus rules.

I'm using the 0.108.0 chart version with the following prometheusRule values:

prometheusRule:
  enabled: true
  groups:
  - name: addtionalCollectorRules
    rules:
    - alert: ExporterQueueFull
      expr: 100 * sum by (exporter) (otelcol_exporter_queue_size) / sum by (exporter) (otelcol_exporter_queue_capacity) > 90
      for: 2m
      labels:
        severity: critical
      annotations:
        description: Queue of exporter {{ $labels.exporter }} is more than 90% full
  defaultRules:
    enabled: true

The helm commands fail (when constructing the templates) with the following error

$ helm template -f values.yaml open-telemetry/opentelemetry-collector --version 0.108.0
Error: YAML parse error on opentelemetry-collector/templates/prometheusrule.yaml: error converting YAML to JSON: yaml: line 25: did not find expected key

Use --debug flag to render out invalid YAML

Running it with the debug flag indeed reveals that the additional group is one indentation level to the right

# Source: opentelemetry-collector/templates/prometheusrule.yaml

apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: release-name-opentelemetry-collector
  namespace: default
  labels:
    helm.sh/chart: opentelemetry-collector-0.108.0
    app.kubernetes.io/name: opentelemetry-collector
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/version: "0.111.0"
    app.kubernetes.io/managed-by: Helm

    release: "kube-prometheus-stack"
spec:
  groups:
    - name: addtionalCollectorRules
      rules:
      - alert: ExporterQueueFull
        annotations:
          description: Queue of exporter {{ $labels.exporter }} is more than 90% full
        expr: 100 * sum by (exporter) (otelcol_exporter_queue_size) / sum by (exporter)
          (otelcol_exporter_queue_capacity) > 90
        for: 2m
        labels:
          severity: critical
  - name: collectorRules
    rules:
    - alert: ReceiverDroppedSpans
      expr: rate(otelcol_receiver_refused_spans[5m]) > 0
      for: 2m
      labels:
        severity: critical
      annotations:
        description: 'The {{ $labels.receiver }} receiver is dropping spans at a rate of {{ humanize $value }} per second '
        runbook_url: 'https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/monitoring.md#receive-failures'
...

Should I pass a different value or different format to groups?

After testing locally, I can create the template without error after changing the line here from

{{- toYaml .Values.prometheusRule.groups | nindent 4 }}

to

{{- toYaml .Values.prometheusRule.groups | nindent 2 }