kubernetes/kops · error

conversion error for field %s: %s

Error message

conversion error for field %s: %s

What it means

During BuildConfigYaml's reflective walk, for every field carrying a `configfile` tag the code resolves the corresponding target field via getValueFromStruct(flagName, target). If that lookup fails, the error is wrapped as "conversion error for field %s". It means the flag name in the configfile tag does not map to a valid field path in the target struct.

Source

Thrown at pkg/configbuilder/buildconfigfile.go:56

		}
		tag := field.Tag.Get("configfile")
		if tag == "" {
			klog.V(4).Infof("not writing field with no configfile tag: %s", path)
			// We want to descend - it could be a structure containing flags
			return nil
		}
		if tag == "-" {
			klog.V(4).Infof("skipping field with %q configfile tag: %s", tag, path)
			return reflectutils.SkipReflection
		}

		tokens := strings.Split(tag, ",")

		flagName := tokens[0]

		targetValue, error := getValueFromStruct(flagName, target)
		if error != nil {
			return fmt.Errorf("conversion error for field %s: %s", flagName, error)
		}
		// We do have to do this, even though the recursive walk will do it for us
		// because when we descend we won't have `field` set
		if val.Kind() == reflect.Ptr {
			if val.IsNil() {
				return nil
			}
		}
		switch v := val.Interface().(type) {
		case *resource.Quantity:
			floatVal, err := strconv.ParseFloat(v.AsDec().String(), 64)
			if err != nil {
				return fmt.Errorf("unable to convert from Quantity %v to float", v)
			}
			targetValue.Set(reflect.ValueOf(&floatVal))
		default:
			targetValue.Set(val)
		}

View on GitHub (pinned to 4c8573c808)

Solutions

1. Check the `configfile` tag of the field named in the error and compare it with the actual field names in the target struct
2. Fix the dotted flag path in the tag so each segment matches a real exported struct field (FieldByName is case-sensitive)
3. If the target field was removed upstream, either add it back to the target struct or drop/rename the configfile tag
4. Add a unit test walking BuildConfigYaml over the full options struct to catch tag/target mismatches early

Example fix

// before
KubeLeaderElection *KubeLeaderElection `json:"leaderElection,omitempty" configfile:"leader-elect"`
// after (target has LeaderElect under LeaderElection struct)
KubeLeaderElection *KubeLeaderElection `json:"leaderElection,omitempty" configfile:"leaderElection.LeaderElect"`

func tagTargetsExist(options interface{}, target interface{}) error {
	var errs []string
	walkTags(options, func(path, tag string) {
		if tag == "" || tag == "-" { return }
		flag := strings.Split(tag, ",")[0]
		if _, err := getValueFromStruct(flag, target); err != nil {
			errs = append(errs, fmt.Sprintf("%s -> %q: %v", path, flag, err))
		}
	})
	if len(errs) > 0 { return fmt.Errorf(strings.Join(errs, "; ")) }
	return nil
}

targetValue, err := getValueFromStruct(flagName, target)
if err != nil {
	return fmt.Errorf("conversion error for field %s: %w", flagName, err)
}

When it happens

Trigger: A `configfile:"some.flag"` struct tag on a KubeSchedulerConfig field names a dotted path whose field does not exist in the target struct, or the path traverses through a non-struct (e.g. a map, slice, or interface) before reaching the named field.

Common situations: Renaming a field in the target config struct (e.g. a component-config type from apimachinery) without updating the configfile tag; adding a new tagged field to KubeSchedulerConfig whose flag name was mistyped; version drift between kops' KubeSchedulerConfig and the upstream component config struct.

Related errors

• only accepts structs; got %T
• unable to convert from Quantity %v to float
• BuildFlagsList to reflect value: %s
• cannot parse flag spec: %q
• unhandled type %v %q

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/26cc2a5fb8da6236. Report an issue: GitHub.