grpc/grpc-go · error

xds_wrr_locality: invalid LBConfig: %s, error: %v

Error message

xds_wrr_locality: invalid LBConfig: %s, error: %v

What it means

Returned by the wrr_locality balancer's ParseConfig (internal/xds/balancer/wrrlocality/balancer.go:94) when json.Unmarshal of the raw LBConfig into *LBConfig fails. The most common cause is malformed JSON or a structurally invalid `childPolicy` field.

Source

Thrown at internal/xds/balancer/wrrlocality/balancer.go:95

	wtbCfgParser, ok := builder.(balancer.ConfigParser)
	if !ok {
		// Shouldn't happen, imported weighted target builder has this method.
		return nil
	}
	wrrL := &wrrLocalityBalancer{
		child:       wtb,
		childParser: wtbCfgParser,
	}

	wrrL.logger = prefixLogger(wrrL)
	wrrL.logger.Infof("Created")
	return wrrL
}

func (bb) ParseConfig(s json.RawMessage) (serviceconfig.LoadBalancingConfig, error) {
	var lbCfg *LBConfig
	if err := json.Unmarshal(s, &lbCfg); err != nil {
		return nil, fmt.Errorf("xds_wrr_locality: invalid LBConfig: %s, error: %v", string(s), err)
	}
	if lbCfg == nil || lbCfg.ChildPolicy == nil {
		return nil, errors.New("xds_wrr_locality: invalid LBConfig: child policy field must be set")
	}
	return lbCfg, nil
}

type attributeKey struct{}

// Equal allows the values to be compared by Attributes.Equal.
func (a AddrInfo) Equal(o any) bool {
	oa, ok := o.(AddrInfo)
	return ok && oa.LocalityWeight == a.LocalityWeight
}

// AddrInfo is the locality weight of the locality an address is a part of.
type AddrInfo struct {
	LocalityWeight uint32

View on GitHub (pinned to 03255a9237)

Solutions

  1. Validate the raw JSON parses before calling ParseConfig
  2. Ensure `childPolicy` is a well-formed BalancerConfig object
  3. Correct the upstream xDS resource emitting the malformed config

Example fix

// before
{"childPolicy":"round_robin"}   // string, not a config object
// after
{"childPolicy":[{"round_robin":{}}]}
Defensive patterns

Strategy: validation

Validate before calling

// Reject malformed JSON before ParseConfig.
if !json.Valid(raw) {
    return fmt.Errorf("wrr_locality config is not valid JSON: %s", string(raw))
}

Type guard

func isWrrLocalityConfig(raw json.RawMessage) bool {
    var probe struct{ ChildPolicy json.RawMessage `json:"childPolicy"` }
    return json.Unmarshal(raw, &probe) == nil && probe.ChildPolicy != nil
}

Try / catch

cfg, err := wrrLocalityBB.ParseConfig(raw)
if err != nil {
    logger.Warningf("rejecting wrr_locality config: %v", err)
    return fallbackLBConfig
}

Prevention

When it happens

Trigger: ParseConfig is given JSON that does not unmarshal into the wrr_locality LBConfig shape — e.g. a JSON syntax error, or `childPolicy` present but not a valid BalancerConfig object.

Common situations: Control plane sends a corrupt Cluster config; hand-built service config with a JSON typo; version skew where the config shape changed.

Related errors

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/82a9469e07d62437. Report an issue: GitHub.