monitoring: Configure KSM & cluster dashboard

[darkowlzz]

NOTE: These changes are added in the new flux2-monitoring-examples repository - fluxcd/flux2-monitoring-example#1 .

The motivation behind this change is to move the responsibility of custom resource metrics to kube-state-metrics (KSM) instead of the individual controllers. The controllers will continue to export metrics about reconciliation and other controller specific metrics. All the metrics about resources that are available on the CRD are exported using KSM. This will allow users to configure custom metrics as per their needs without any changes in the controllers. This will also allow us to have static resources that don't have a reconciler for reporting resource readiness metrics but continue to have the same monitoring capabilities, for example the HelmRepository source resource in OCI mode, Alert and Provider notification resources, and other upcoming API resources that may not be backed by reconcilers.

Update kube-prometheus-stack helm release values to configure kube-state-metrics and use kube-state-metrics to collect gotk resource state metrics.

• Configure kube-state-metrics to run in custom resource state only mode. In this mode, it'll only watch custom resources. Also, pass empty collectors as extra args to prevent passing all the core resources to watch as an argument.
• Running kube-state-metrics in custom resource state only mode makes the default grafana dashboards of no use. Disable the default dashboards.
• Add kube-state-metrics configuration to provide RBAC permissions to it to allow listing and watching flux CRDs.
• Also, configure custom resource state for each of the flux custom resources using Info type metrics called gotk_resource_info. KSM issues a warning if an Info type object doesn't have _info suffix. These metrics have the value 1 always. This works well for the CRD state metrics as a zero value would mean that the resource doesn't exist, in which case, the resource is deleted.
• Update the cluster dashboard panels to use gotk_resource_info in the queries.
  • Only the following panels have been updated
    • Cluster Reconcilers
    • Failing Reconcilers
    • Cluster reconciliation readiness
    • Kubernetes Manifests Sources
    • Failing Sources
    • Source acquisition readiness
  • The panels have been updated such that it's work with static resources which don't have any status as well. By default, it assumes such static resources to be in a Ready state. Resources are seen as failed only when the ready value is false.
  • The queries have been updated to Instant type in order to show the current data, instead of the result of past 15 minutes. This shows more accurate resource data as the resource metrics change.
  • The Stat visualizers have been updated to have zero as the default value when there's no data. This is to prevent showing no data when there's no object. This was motivated by the behavior of the previous configuration which depended on stale metrics from controllers and deleted conditions to show zero value when objects get deleted. With the fixes in the controller metrics that removes stale metrics, this will no longer work. In order to show a zero value for these stats, a default is set.
  • The $namespace variable has been updated to refer to exported_namespace from gotk_resource_info.

Sample resource metrics from KSM:

# HELP gotk_resource_info The current state of a GitOps Toolkit resource.
# TYPE gotk_resource_info info
gotk_resource_info{customresource_group="kustomize.toolkit.fluxcd.io",customresource_kind="Kustomization",customresource_version="v1",exported_namespace="default",name="podinfo",ready="True"} 1
gotk_resource_info{customresource_group="source.toolkit.fluxcd.io",customresource_kind="GitRepository",customresource_version="v1",exported_namespace="monitoring",name="test-2",ready="True"} 1
gotk_resource_info{customresource_group="source.toolkit.fluxcd.io",customresource_kind="GitRepository",customresource_version="v1",exported_namespace="default",name="test-1",ready="True"} 1
gotk_resource_info{customresource_group="source.toolkit.fluxcd.io",customresource_kind="HelmChart",customresource_version="v1beta2",exported_namespace="default",name="podinfo",ready="True"} 1
gotk_resource_info{customresource_group="source.toolkit.fluxcd.io",customresource_kind="HelmRepository",customresource_version="v1beta2",exported_namespace="default",name="podinfo",ready="True"} 1

The dashboard is identical to the existing dashboard with slight differences:

Kube-state-metrics custom-resource state metrics docs: https://github.com/kubernetes/kube-state-metrics/blob/main/docs/customresourcestate-metrics.md

[stefanprodan]

Moved to https://github.com/fluxcd/flux2-monitoring-example