LB policy name %q found in Children field (%v) is not found

Error message

LB policy name %q found in Children field (%v) is not found in Priorities field (%+v)

What it means

Returned by the priority balancer's parseConfig (internal/xds/balancer/priority/config.go:62) when a key exists in the `children` map but is not listed in the `priorities` array. Every defined child must appear in priorities; an orphaned child is rejected.

Source

Thrown at internal/xds/balancer/priority/config.go:63

	Priorities []string `json:"priorities,omitempty"`
}

func parseConfig(c json.RawMessage) (*LBConfig, error) {
	var cfg LBConfig
	if err := json.Unmarshal(c, &cfg); err != nil {
		return nil, err
	}

	prioritiesSet := make(map[string]bool)
	for _, name := range cfg.Priorities {
		if _, ok := cfg.Children[name]; !ok {
			return nil, fmt.Errorf("LB policy name %q found in Priorities field (%v) is not found in Children field (%+v)", name, cfg.Priorities, cfg.Children)
		}
		prioritiesSet[name] = true
	}
	for name := range cfg.Children {
		if _, ok := prioritiesSet[name]; !ok {
			return nil, fmt.Errorf("LB policy name %q found in Children field (%v) is not found in Priorities field (%+v)", name, cfg.Children, cfg.Priorities)
		}
	}
	return &cfg, nil
}

View on GitHub (pinned to 03255a9237)

Solutions

Add every child name to the `priorities` list, or remove unused children
Correct the upstream xDS resource to keep children and priorities in sync
Validate that the children key set equals the priorities set before publishing

Example fix

// before
{"children":{"a":{...},"b":{...}},"priorities":["a"]}
// after
{"children":{"a":{...},"b":{...}},"priorities":["a","b"]}

Defensive patterns

Strategy: validation

Validate before calling

var probe struct {
    Children   map[string]json.RawMessage `json:"children"`
    Priorities []string                   `json:"priorities"`
}
_ = json.Unmarshal(raw, &probe)
pset := make(map[string]bool, len(probe.Priorities))
for _, p := range probe.Priorities { pset[p] = true }
for name := range probe.Children {
    if !pset[name] {
        return fmt.Errorf("child %q is not listed in priorities", name)
    }
}

Try / catch

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

Prevention

Keep the children map and priorities list in lockstep
Remove children when dropping them from priorities

When it happens

Trigger: parseConfig receives JSON where `children` defines a name that does not appear in `priorities` — e.g. children:{"a","b"} but priorities:["a"].

Common situations: Control plane adds a child but forgets to add it to priorities; typo in the priorities list; stale child left in the map after a priorities edit.

Related errors

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/6c4d3c6964f8aab8. Report an issue: GitHub.