Why is MinReplicas a pointer type in the resource definition of HorizontalPodAutoscaler, while MaxReplicas is an int32 type

ZhangSetSail · July 6, 2022, 11:58am

kubernetes/kubernetes/blob/ea0764452222146c47ec826977f49d7001b0ea8c/pkg/apis/autoscaling/types.go#L75


      
          	// Kind of the referent; More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds"
          	Kind string
          	// Name of the referent; More info: http://kubernetes.io/docs/user-guide/identifiers#names
          	Name string
          	// API version of the referent
          	// +optional
          	APIVersion string
          }
          
          
// HorizontalPodAutoscalerSpec describes the desired functionality of the HorizontalPodAutoscaler.
          type HorizontalPodAutoscalerSpec struct {
          	// ScaleTargetRef points to the target resource to scale, and is used to the pods for which metrics
          	// should be collected, as well as to actually change the replica count.
          	ScaleTargetRef CrossVersionObjectReference
          	// minReplicas is the lower limit for the number of replicas to which the autoscaler
          	// can scale down.  It defaults to 1 pod.  minReplicas is allowed to be 0 if the
          	// alpha feature gate HPAScaleToZero is enabled and at least one Object or External
          	// metric is configured.  Scaling is active as long as at least one metric value is
          	// available.
          	// +optional
          	MinReplicas *int32

thockin · July 6, 2022, 2:58pm

Because min can be 0 (it’s not common but allowed), but that is Go’s default value which means we can’t tell if it was set to 0 but the user or just left unspecified (in which case the default is documented as 1).

TLDR - implementation detail leaking through

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Why is MinReplicas a pointer type in the resource definition of HorizontalPodAutoscaler, while MaxReplicas is an int32 type

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