✨ metrics: add generator for kube-state-metrics customresource configuration

[chrischdi]

This adds a generator to generate a customresource configuration file for kube-state-metrics from markers.

With that configuration it is possible to get metrics for CRs like kube-state-metrics exposes for core resources.
(xref)

Example usage:

controller-gen metrics output:metrics:stdout \
     paths=./api/...\
     > crd-config.yaml

Introduced markers:

$ controller-gen metrics -ww

Metric type Gauge


+Metrics:gauge type
	defines a Gauge metric and uses the implicit path to the field joined by the provided JSONPath as path for the metric configuration.
	[JSONPath=<string>]      specifies the relative path from this marker.                                          
	[help=<string>]          specifies the help text for the metric.                                                
	[labelFromKey=<string>]  specifies a label which will be added to the metric having the object's key as value.  
	[labelsFromPath=<>]      specifies additional labels where the value is taken from the given JSONPath.          
	name=<string>            specifies the Name of the metric.                                                      
	[nilIsZero=<bool>]       specifies to treat a not-existing field as zero value.                                 
	[valueFrom=<string>]     specifies the JSONPath to a numeric field that will be the metric value.               

+Metrics:gauge field
	defines a Gauge metric and uses the implicit path to the field joined by the provided JSONPath as path for the metric configuration.
	[JSONPath=<string>]      specifies the relative path from this marker.                                          
	[help=<string>]          specifies the help text for the metric.                                                
	[labelFromKey=<string>]  specifies a label which will be added to the metric having the object's key as value.  
	[labelsFromPath=<>]      specifies additional labels where the value is taken from the given JSONPath.          
	name=<string>            specifies the Name of the metric.                                                      
	[nilIsZero=<bool>]       specifies to treat a not-existing field as zero value.                                 
	[valueFrom=<string>]     specifies the JSONPath to a numeric field that will be the metric value.               

Metric type Info


+Metrics:info type
	defines a Info metric and uses the implicit path to the field as path for the metric configuration.
	[JSONPath=<string>]      specifies the relative path from this marker.                                          
	[help=<string>]          specifies the help text for the metric.                                                
	[labelFromKey=<string>]  specifies a label which will be added to the metric having the object's key as value.  
	[labelsFromPath=<>]      specifies additional labels where the value is taken from the given JSONPath.          
	name=<string>            specifies the Name of the metric.                                                      

+Metrics:info field
	defines a Info metric and uses the implicit path to the field as path for the metric configuration.
	[JSONPath=<string>]      specifies the relative path from this marker.                                          
	[help=<string>]          specifies the help text for the metric.                                                
	[labelFromKey=<string>]  specifies a label which will be added to the metric having the object's key as value.  
	[labelsFromPath=<>]      specifies additional labels where the value is taken from the given JSONPath.          
	name=<string>            specifies the Name of the metric.                                                      

Metric type StateSet


+Metrics:stateset type
	defines a StateSet metric and uses the implicit path to the field as path for the metric configuration.
	[JSONPath=<string>]   specifies the path to the field which gets used as value to compare against the list for equality.  
	[help=<string>]       specifies the help text for the metric.                                                             
	[labelName=<string>]  specifies the key of the label which is used for each entry in List to expose the value.            
	[labelsFromPath=<>]   specifies additional labels where the value is taken from the given JSONPath.                       
	list=<[]string>       specifies a list of values to compare the given JSONPath against.                                   
	name=<string>         specifies the Name of the metric.                                                                   

+Metrics:stateset field
	defines a StateSet metric and uses the implicit path to the field as path for the metric configuration.
	[JSONPath=<string>]   specifies the path to the field which gets used as value to compare against the list for equality.  
	[help=<string>]       specifies the help text for the metric.                                                             
	[labelName=<string>]  specifies the key of the label which is used for each entry in List to expose the value.            
	[labelsFromPath=<>]   specifies additional labels where the value is taken from the given JSONPath.                       
	list=<[]string>       specifies a list of values to compare the given JSONPath against.                                   
	name=<string>         specifies the Name of the metric.                                                                   

Metrics


+Metrics:gvk type
	enables the creation of a custom resource configuration entry and uses the given prefix for the metrics if configured.
	[namePrefix=<string>]  specifies the prefix for all metrics of this resource.  

+Metrics:labelFromPath type
	specifies additional labels for all metrics of this field or type.
	JSONPath=<string>  specifies the path to the value for the label.  
	name=<string>      specifies the name of the label.                

+Metrics:labelFromPath field
	specifies additional labels for all metrics of this field or type.
	JSONPath=<string>  specifies the path to the value for the label.  
	name=<string>      specifies the name of the label.                

Example usage: kubernetes-sigs/cluster-api#9347

[chrischdi]

If wanted, I can volunteer to maintain this part of controller-gen (and/or also help on other parts of controller-tools) :-)

[sbueringer]

We'll get back to this eventually, just low bandwith at the moment

[k8s-triage-robot]

The Kubernetes project currently lacks enough contributors to adequately respond to all PRs.

This bot triages PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the PR is closed

You can:

• Mark this PR as fresh with /remove-lifecycle stale
• Close this PR with /close
• Offer to help out with Issue Triage

Please send feedback to sig-contributor-experience at kubernetes/community.

/lifecycle stale

[sbueringer]

/remove-lifecycle stale

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: chrischdi
Once this PR has been reviewed and has the lgtm label, please assign alvaroaleman for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment