grpc/grpc-go · error

no children to pick from

Error message

no children to pick from

What it means

Internal error produced by the endpointsharding balancer (balancer/endpointsharding/endpointsharding.go:291-294) when its children list is empty — there are zero child balancers to pick from. It wraps the message in a base.NewErrPicker and aggregates to TransientFailure. The inline comment 'No children (resolver error before valid update)' describes the cause.

Source

Thrown at balancer/endpointsharding/endpointsharding.go:293

	// the aggregated state, use the pickers present that are currently in that
	// state only.
	var aggState connectivity.State
	var pickers []balancer.Picker
	if len(readyPickers) >= 1 {
		aggState = connectivity.Ready
		pickers = readyPickers
	} else if len(connectingPickers) >= 1 {
		aggState = connectivity.Connecting
		pickers = connectingPickers
	} else if len(idlePickers) >= 1 {
		aggState = connectivity.Idle
		pickers = idlePickers
	} else if len(transientFailurePickers) >= 1 {
		aggState = connectivity.TransientFailure
		pickers = transientFailurePickers
	} else {
		aggState = connectivity.TransientFailure
		pickers = []balancer.Picker{base.NewErrPicker(errors.New("no children to pick from"))}
	} // No children (resolver error before valid update).
	p := &pickerWithChildStates{
		pickers:     pickers,
		childStates: childStates,
		next:        uint32(randIntN(len(pickers))),
	}
	es.cc.UpdateState(balancer.State{
		ConnectivityState: aggState,
		Picker:            p,
	})
}

// pickerWithChildStates delegates to the pickers it holds in a round robin
// fashion. It also contains the childStates of all the endpointSharding's
// children.
type pickerWithChildStates struct {
	pickers     []balancer.Picker
	childStates []ChildState

View on GitHub (pinned to 03255a9237)

Solutions

1. Ensure the resolver actually supplies endpoints — endpointsharding keys children off resolver.State.Endpoints, so an empty Endpoints slice yields no children.
2. Wait for the first valid resolver/LB update before issuing RPCs, or use grpc.WaitForReady(true).
3. If configuring endpointsharding directly, confirm childPolicy and the endpoint list are populated; check the parent policy (xDS resource exists and is healthy).
4. Look at channelz / connectivity: a persistent TransientFailure with this picker means upstream resolution never succeeded — fix the resolver/control plane.

Example fix

// before — issuing RPC immediately on a channel whose endpoint source is empty
client := grpc.NewClient("xds:///missing-resource")
client.SayHello(ctx, req) // -> Unavailable: no children to pick from

// after — wait for ready and verify endpoints arrive
client := grpc.NewClient("xds:///valid-resource")
client.Connect() // trigger exit-idle / resolution
client.SayHello(ctx, req, grpc.WaitForReady(true))

// Ensure endpoints exist before issuing RPCs on an endpointsharding channel
rs, _ := resolver.Get(scheme).Build(...).ResolveNow(...) // or check your resolver emits Endpoints
if len(rs.Endpoints) == 0 {
    return errors.New("no endpoints; endpointsharding will have no children")
}

if strings.Contains(err.Error(), "no children to pick from") {
    // upstream resolution produced no endpoints; wait or fix resolver/control plane
}

When it happens

Trigger: endpointsharding.generatePickerState finds no children at all: len(readyPickers)+connecting+idle+transientFailure all zero. This happens before the first valid resolver update delivers any endpoint, or after every endpoint/child has been removed.

Common situations: Used as a sub-policy (e.g. under xds / cluster_resolver / weightedtarget) before the first xDS response; resolver returned resolver.State with no Endpoints; all endpoints drained during a config update; misconfigured endpointsharding with no child policy producing children.

Related errors

• bad resolver state
• no SubConn is available
• all SubConns are in TransientFailure
• weighted-target: no targets to pick from
• last resolver error: %v

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/3f5dc3ba51a464f1. Report an issue: GitHub.