Add validation to `CRDUpgradeSafety` preflight check to allow decreasing minimum values on existing fields

[Bryce Palmer]

Now that there is a base CRDUpgradeSafety preflight check in place, we can continue adding validation logic based on the CRDUpgradeSafety preflight check proposal.

This issue focuses on adding a validation to ensure that updates to an existing field are allowed when the update performed is a decrease in the minimum allowed values.

As a potential source of inspiration, here is how a couple of the existing validations are implemented:

• Definitions:

  kapp/pkg/kapp/crdupgradesafety/validator.go

  Lines 71 to 93 in 82f2a30

   func NoScopeChange(old, new v1.CustomResourceDefinition) error { 
   	if old.Spec.Scope != new.Spec.Scope { 
   		return fmt.Errorf("scope changed from %q to %q", old.Spec.Scope, new.Spec.Scope) 
   	} 
   	return nil 
   } 
    
   func NoStoredVersionRemoved(old, new v1.CustomResourceDefinition) error { 
   	newVersions := sets.New[string]() 
   	for _, version := range new.Spec.Versions { 
   		if !newVersions.Has(version.Name) { 
   			newVersions.Insert(version.Name) 
   		} 
   	} 
    
   	for _, storedVersion := range old.Status.StoredVersions { 
   		if !newVersions.Has(storedVersion) { 
   			return fmt.Errorf("stored version %q removed", storedVersion) 
   		} 
   	} 
    
   	return nil 
   } 

• Consumption:

  kapp/pkg/kapp/crdupgradesafety/preflight.go

  Lines 36 to 39 in 82f2a30

   Validations: []Validation{ 
   	NewValidationFunc("NoScopeChange", NoScopeChange), 
   	NewValidationFunc("NoStoredVersionRemoved", NoStoredVersionRemoved), 
   }, 

Note

It may be useful to consider a more generic check that allows for easily extending the validations that are run against updates to existing fields in a CRD schema