Immutable fields advisory (#70)

Add an advisory condition if an immutable field is modified.

```
  Conditions:
    Status:     False
    Type:       ACK.Terminal
    Status:     True
    Type:       ACK.ResourceSynced
    Status:     False
    Type:       ACK.Recoverable
    Message:    Immutable Spec fields have been modified : AtRestEncryptionEnabled,TransitEncryptionEnabled
    Status:     True
    Type:       ACK.Advisory
  Description:  Reinvent replication group
```

Clears the status upon fixing the field in the manifest

```
  Conditions:
    Status:     False
    Type:       ACK.Terminal
    Status:     True
    Type:       ACK.ResourceSynced
    Status:     False
    Type:       ACK.Recoverable
  Description:  Reinvent replication group
```

This commit allows one to specify immutable fields in `generator.yaml`.

```
      TransitEncryptionEnabled:
        is_immutable: true
      AtRestEncryptionEnabled:
        is_immutable: true
```

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: nmvk

pkg/generate/config/field.go

@@ -155,6 +155,9 @@ type FieldConfig struct {
 	// IsSecret instructs the code generator that this field should be a
 	// SecretKeyReference.
 	IsSecret bool `json:"is_secret"`
+	// IsImmutable instructs the code generator to add advisory conditions
+	// if user modifies the spec field after resource was created.
+	IsImmutable bool `json:"is_immutable"`
 	// From instructs the code generator that the value of the field should
 	// be retrieved from the specified operation and member path
 	From *SourceFieldConfig `json:"from,omitempty"`

pkg/model/crd.go

@@ -303,6 +303,32 @@ func (r *CRD) IsSecretField(path string) bool {
 	return false
 }
 
+// GetImmutableFieldPaths returns list of immutable field paths present in CRD
+func (r *CRD) GetImmutableFieldPaths() []string {
+	fConfigs := r.cfg.ResourceFields(r.Names.Original)
+	var immutableFields []string
+
+	for field, fieldConfig := range fConfigs {
+		if fieldConfig.IsImmutable {
+			immutableFields = append(immutableFields, field)
+		}
+	}
+
+	return immutableFields
+}
+
+// HasImmutableFieldChanges helper function that return true if there are any immutable field changes
+func (r *CRD) HasImmutableFieldChanges() bool {
+	fConfigs := r.cfg.ResourceFields(r.Names.Original)
+
+	for _, fieldConfig := range fConfigs {
+		if fieldConfig.IsImmutable {
+			return true
+		}
+	}
+	return false
+}
+
 // SetOutputCustomMethodName returns custom set output operation as *string for
 // given operation on custom resource, if specified in generator config
 func (r *CRD) SetOutputCustomMethodName(

templates/pkg/resource/sdk.go.tpl

@@ -276,3 +276,63 @@ func (rm *resourceManager) terminalAWSError(err error) bool {
 	return false
 {{- end }}
 }
+
+{{- if .CRD.HasImmutableFieldChanges }}
+// getImmutableFieldChanges returns list of immutable fields from the
+func (rm *resourceManager) getImmutableFieldChanges(
+	delta *ackcompare.Delta,
+) []string {
+	var fields []string;
+
+	{{- range $immutableField := .CRD.GetImmutableFieldPaths }}
+		if delta.DifferentAt("{{$immutableField}}") {
+			fields = append(fields,"{{$immutableField}}")
+		}
+	{{- end }}
+
+	return fields
+}
+
+// handleImmutableFieldsChangedCondition validates the immutable fields and set appropriate condition
+func (rm *resourceManager) handleImmutableFieldsChangedCondition(
+	r *resource,
+	delta *ackcompare.Delta,
+) *resource {
+
+	fields := rm.getImmutableFieldChanges(delta)
+	ko := r.ko.DeepCopy()
+	var advisoryCondition *ackv1alpha1.Condition = nil
+	for _, condition := range ko.Status.Conditions {
+		if condition.Type == ackv1alpha1.ConditionTypeAdvisory {
+			advisoryCondition = condition
+			break
+		}
+	}
+
+	// Remove the advisory condition if issue is no longer present
+	if len(fields) == 0 && advisoryCondition != nil{
+		var newConditions []*ackv1alpha1.Condition
+		for _, condition := range ko.Status.Conditions {
+			if condition.Type != ackv1alpha1.ConditionTypeAdvisory {
+				newConditions = append(newConditions,condition)
+			}
+		}
+		ko.Status.Conditions = newConditions
+	}
+
+	if len(fields) > 0 {
+		if advisoryCondition == nil {
+			advisoryCondition = &ackv1alpha1.Condition{
+				Type: ackv1alpha1.ConditionTypeAdvisory,
+			}
+			ko.Status.Conditions = append(ko.Status.Conditions, advisoryCondition)
+		}
+
+		advisoryCondition.Status = corev1.ConditionTrue
+		message := "Immutable Spec fields have been modified : " + strings.Join(fields, ",")
+		advisoryCondition.Message = &message
+	}
+
+	return &resource{ko}
+}
+{{- end }}

templates/pkg/resource/sdk_update.go.tpl

@@ -32,6 +32,9 @@ func (rm *resourceManager) sdkUpdate(
 	if respErr != nil {
 		return nil, respErr
 	}
+{{- if .CRD.HasImmutableFieldChanges }}
+	desired = rm.handleImmutableFieldsChangedCondition(desired, delta)
+{{- end }}
 	// Merge in the information we read from the API call above to the copy of
 	// the original Kubernetes object we passed to the function
 	ko := desired.ko.DeepCopy()