CRD Custom Exporter

Expose custom CRD fields as prometheus metrics

Proposal

Disclaimer: this is my very first kubernetes focused project, so be gentle please :)

This is an initial proposal to expose Kubernetes' Custom Resource Definitions (CRD) as Prometheus metrics endpoints. The aim is to monitore and alert on whatever an Custom Resource (CR) exposes, by using a simple property -> metric mapping model.

Supose we have the following Velero Schedule CR (incomplete for readability):

apiVersion: velero.io/v1
kind: Schedule
metadata:
  name: shopping
  namespace: megastore
spec:
  schedule: 0 3 * * *
  template:
    includeClusterResources: true
    includedNamespaces:
    - webapp
    - database
    includedResources:
    - deployments
    - cronjobs

In order to expose metrics regarding includedNamespaces, one could define the following config:

customResourceDefinitions:
- apiVersion: velero.io/v1
  kind: Schedule
  inspect:
  - included_namespaces: spec.template.includedNamespaces

or maybe:

customResourceDefinitions:
- apiVersion: velero.io/v1
  kind: Schedule
  spec:
    template:
      includedNamespaces:
      - webapp
      - database
      - non-existing

Which will generate the following prometheus metrics:

crd_exporter_velero_io_v1_included_namespaces_webapp{namespace="megastore", name="shopping"} 1
crd_exporter_velero_io_v1_included_namespaces_database{namespace="megastore" ,name="shopping"} 1

or maybe

crd_exporter_schedule_velero_io_included_namespaces_webapp{namespace="megastore", name="shopping", crd="schedule", api_group="velero.io", api_version="v1"} 1
crd_exporter_schedule_velero_included_namespaces_database{namespace="megastore", name="shopping", crd="schedule", api_group="velero.io", api_version="v1"} 1

or maybe

crd_exporter_schedule_velero_io{namespace="megastore", name="shopping", crd="schedule", api_group="velero.io", api_version="v1", path="spec.template.includedNamespace[0].webapp"} 1
crd_exporter_schedule_velero_io{namespace="megastore", name="shopping", crd="schedule", api_group="velero.io", api_version="v1", path="spec.template.includedNamespace[1].database"} 1
crd_exporter_schedule_velero_io{namespace="megastore", name="shopping", crd="schedule", api_group="velero.io", api_version="v1", path="spec.template.includedNamespace[2].non-existing"} 0