Does Custom Resource State Metrics support deep nested objects?

[pbxqdown]

We have a k8s object as follows.

status:
    resourceCount:
      tenantA:
        hostGroupA:
          example.com/type1: 2
          example.com/type2: 2
          example.com/type3: 20

We would like to generate a metrics like resourceCount{tenant=tenantA, hostGroup=hostGroupA, resourceType=type2} 2.
Initially I tried to use labelFromKey, but it seems only supports one level of nesting. I have to statically specify path, and in the last level use labelFromKey to generate metrics by resourceType.

metrics:
            - name: resourceCount
              each:
                type: Gauge
                gauge:
                  path: [status, resourceCount, tenantA, hostGroupA]
                  labelFromKey: resourceType

Wondering whether we can use labelFromKey for nested objects.

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[ringerc]

If I understand correctly, you want the "parent" keys in the CR to be added as labels.

This seems interesting but hard to generalize. How would this work if there are multiple keys with different structures? And when faced with sub-trees containing arrays, how would it know what key to use as the label name and value, and which key to traverse for further values? It seems like you would need something like a JSONPath expression or a series of them, so you could express to k-s-m a generic pattern for traversing your CR to discover unique time-series and values for them.

Otherwise you won't be able to handle something like:

status:
    resourceCount:
      - name: tenantA:
        hosts:
         - hostname: hostGroupA
           entries:
             - type: example.com/type1:
               count: 2
             - type: example.com/type2
               count: 2
             - type: example.com/type3
               count: 20

... which is the other common pattern for expressing these sorts of structures.

[pbxqdown]

Thanks for response @ringerc. Yes I think we need something like JSONPath to extract arbitrary custom info from k8s object. A kubectl request may look like:

kubectl get <resource> -o=jsonpath='{range .status.resourceCount[*]}{range @[*]}{range @}["{.}", "{@}"]{"\n"}{end}{end}{end}'

If there is a general solution for this, kube-state-metrics will be much more powerful. But it is understandable this might be challenging.
We end up with defining prometheus metrics directly inside source code. It feels easier than configuring kube-state-metrics to expose highly customized objects.

[Dentrax]

Duplicate of #2368