xds_wrr_locality: missing locality weight information in end

Error message

xds_wrr_locality: missing locality weight information in endpoint %q

What it means

Returned by wrr_locality UpdateClientConnState (internal/xds/balancer/wrrlocality/balancer.go:170) when an endpoint in the resolver state has no AddrInfo attribute (no locality weight). The xDS resolver normally attaches AddrInfo with the locality weight to every endpoint; wrr_locality needs it to build weighted targets per locality.

Source

Thrown at internal/xds/balancer/wrrlocality/balancer.go:170

}

func (b *wrrLocalityBalancer) UpdateClientConnState(s balancer.ClientConnState) error {
	lbCfg, ok := s.BalancerConfig.(*LBConfig)
	if !ok {
		b.logger.Errorf("Received config with unexpected type %T: %v", s.BalancerConfig, s.BalancerConfig)
		return balancer.ErrBadResolverState
	}

	weightedTargets := make(map[string]weightedtarget.Target)
	for _, ep := range s.ResolverState.Endpoints {
		// This get of LocalityID could potentially return a zero value. This
		// shouldn't happen though (this attribute that is set actually gets
		// used to build localities in the first place), and thus don't error
		// out, and just build a weighted target with undefined behavior.
		locality := xdsinternal.LocalityString(xdsinternal.LocalityIDFromEndpoint(ep))
		ai, ok := getAddrInfo(ep)
		if !ok {
			return fmt.Errorf("xds_wrr_locality: missing locality weight information in endpoint %q", ep)
		}
		weightedTargets[locality] = weightedtarget.Target{Weight: ai.LocalityWeight, ChildPolicy: lbCfg.ChildPolicy}
	}
	wtCfg := &weightedtarget.LBConfig{Targets: weightedTargets}
	wtCfgJSON, err := json.Marshal(wtCfg)
	if err != nil {
		// Shouldn't happen.
		return fmt.Errorf("xds_wrr_locality: error marshalling prepared config: %v", wtCfg)
	}
	var sc serviceconfig.LoadBalancingConfig
	if sc, err = b.childParser.ParseConfig(wtCfgJSON); err != nil {
		return fmt.Errorf("xds_wrr_locality: config generated %v is invalid: %v", wtCfgJSON, err)
	}

	return b.child.UpdateClientConnState(balancer.ClientConnState{
		ResolverState:  s.ResolverState,
		BalancerConfig: sc,
	})

View on GitHub (pinned to 03255a9237)

Solutions

Ensure the channel is driven by the xDS resolver so endpoints carry AddrInfo
If building endpoints manually, attach the weight via wrrlocality.SetAddrInfo(ep, AddrInfo{LocalityWeight: w})
Use wrr_locality only within the xDS-managed path

Example fix

// before: endpoint built without locality weight
ep := resolver.Endpoint{...}
// after
import "google.golang.org/grpc/internal/xds/balancer/wrrlocality"
ep := wrrlocality.SetAddrInfo(resolver.Endpoint{...}, wrrlocality.AddrInfo{LocalityWeight: 100})

Defensive patterns

Strategy: validation

Validate before calling

// Ensure every endpoint carries a locality weight before UpdateClientConnState.
for _, ep := range state.ResolverState.Endpoints {
    if _, ok := wrrlocality.GetAddrInfoPublic(ep); !ok {
        return fmt.Errorf("endpoint missing locality weight; not from xDS resolver")
    }
}

Type guard

func endpointsHaveLocalityWeight(eps []resolver.Endpoint) bool {
    for _, ep := range eps {
        v := ep.Attributes.Value(attributeKey{})
        if _, ok := v.(wrrlocality.AddrInfo); !ok {
            return false
        }
    }
    return true
}

Try / catch

if err := bal.UpdateClientConnState(state); err != nil {
    if strings.Contains(err.Error(), "missing locality weight") {
        logger.Errorf("endpoints not produced by xDS resolver; skip wrr_locality: %v", err)
    }
    return err
}

Prevention

Use wrr_locality only behind the xDS resolver
When constructing endpoints manually, call wrrlocality.SetAddrInfo
In tests, always attach AddrInfo to fake endpoints

When it happens

Trigger: UpdateClientConnState iterates endpoints and getAddrInfo(ep) returns ok=false for one of them, meaning the resolver did not call SetAddrInfo to attach a LocalityWeight attribute. This should not happen in the real xDS flow; it indicates the resolver state was not produced by the xDS resolver.

Common situations: A non-xDS resolver feeds endpoints into a channel using the wrr_locality policy; the xDS resolver was bypassed or a custom resolver omitted the locality weight attribute; a partially-mocked resolver in tests.

Related errors

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/d48f695305c7d713. Report an issue: GitHub.