Prevent multiple custom resource configurations for the same resource

Author: chrischdi

docs/customresourcestate-metrics.md

@@ -9,12 +9,14 @@ A YAML configuration file described below is required to define your custom reso
 
 Two flags can be used:
 
- * `--custom-resource-state-config "inline yaml (see example)"` or
- * `--custom-resource-state-config-file /path/to/config.yaml`
+* `--custom-resource-state-config "inline yaml (see example)"` or
+* `--custom-resource-state-config-file /path/to/config.yaml`
 
 If both flags are provided, the inline configuration will take precedence.
+When multiple entries for the same resource exist, kube-state-metrics will exit with an error.
+This includes configuration which refers to a different API version.
 
-In addition to specifying one of `--custom-resource-state-config*` flags, you should also add the custom resource *Kind*s in plural form to the list of exposed resources in the `--resources` flag. If you don't specify `--resources`, then all known custom resources configured in `--custom-resource-state-config-*` and all available default kubernetes objects will be taken into account by kube-state-metrics.
+In addition to specifying one of `--custom-resource-state-config*` flags, you should also add the custom resource *Kind*s in plural form to the list of exposed resources in the `--resources` flag. If you don't specify `--resources`, then all known custom resources configured in `--custom-resource-state-config*` and all available default kubernetes objects will be taken into account by kube-state-metrics.
 
 ```yaml
 apiVersion: apps/v1

pkg/customresourcestate/config.go

@@ -162,8 +162,10 @@ type ConfigDecoder interface {
 }
 
 // FromConfig decodes a configuration source into a slice of customresource.RegistryFactory that are ready to use.
-func FromConfig(decoder ConfigDecoder) (factories []customresource.RegistryFactory, err error) {
+func FromConfig(decoder ConfigDecoder) ([]customresource.RegistryFactory, error) {
 	var crconfig Metrics
+	var factories []customresource.RegistryFactory
+	factoriesIndex := map[string]bool{}
 	if err := decoder.Decode(&crconfig); err != nil {
 		return nil, fmt.Errorf("failed to parse Custom Resource State metrics: %w", err)
 	}
@@ -172,6 +174,10 @@ func FromConfig(decoder ConfigDecoder) (factories []customresource.RegistryFacto
 		if err != nil {
 			return nil, fmt.Errorf("failed to create metrics factory for %s: %w", resource.GroupVersionKind, err)
 		}
+		if _, ok := factoriesIndex[factory.Name()]; ok {
+			return nil, fmt.Errorf("found multiple custom resource configurations for the same resource %s", factory.Name())
+		}
+		factoriesIndex[factory.Name()] = true
 		factories = append(factories, factory)
 	}
 	return factories, nil