grpc/grpc-go · error

rls_csp: error marshaling load balancing config %v: %v

Error message

rls_csp: error marshaling load balancing config %v: %v

What it means

Returned when encoding/json.Marshal of the internally constructed lbConfigJSON (RouteLookupConfig raw JSON + hardcoded child policy) fails. Because all fields are built from controlled types, this is effectively an internal/programmer error and should not occur in normal operation.

Source

Thrown at internal/xds/clusterspecifier/rls/rls.go:83

		return nil, fmt.Errorf("rls_csp: error parsing config %v: %v", cfg, err)
	}
	rlcJSON, err := protojson.Marshal(rlcs.GetRouteLookupConfig())
	if err != nil {
		return nil, fmt.Errorf("rls_csp: error marshaling route lookup config: %v: %v", rlcs.GetRouteLookupConfig(), err)
	}
	lbCfgJSON := &lbConfigJSON{
		RouteLookupConfig: rlcJSON, // "JSON form of RouteLookupClusterSpecifier.config" - RLS in xDS Design Doc
		ChildPolicy: []map[string]json.RawMessage{
			{
				"cds_experimental": json.RawMessage(`{"isDynamic":true}`),
			},
		},
		ChildPolicyConfigTargetFieldName: "cluster",
	}

	rawJSON, err := json.Marshal(lbCfgJSON)
	if err != nil {
		return nil, fmt.Errorf("rls_csp: error marshaling load balancing config %v: %v", lbCfgJSON, err)
	}

	rlsBB := balancer.Get(internal.RLSLoadBalancingPolicyName)
	if rlsBB == nil {
		return nil, fmt.Errorf("RLS LB policy not registered")
	}
	if _, err = rlsBB.(balancer.ConfigParser).ParseConfig(rawJSON); err != nil {
		return nil, fmt.Errorf("rls_csp: validation error from rls lb policy parsing: %v", err)
	}

	return clusterspecifier.BalancerConfig{{internal.RLSLoadBalancingPolicyName: lbCfgJSON}}, nil
}

View on GitHub (pinned to 03255a9237)

Solutions

1. Report upstream as a bug — the constructed lbConfigJSON should always serialize.
2. If forking the plugin, ensure RouteLookupConfig remains a valid json.RawMessage and childPolicy entries are valid JSON objects.

When it happens

Trigger: A json.RawMessage field inside lbCfgJSON containing invalid JSON, or a type that does not satisfy json.Marshaler — only possible if the hardcoded construction is tampered with or a dependency returns malformed raw JSON.

Common situations: Not seen in production through the xDS path; would indicate a bug in the RLS plugin or a corrupted build. Treat as a defect to report.

Related errors

• rls_csp: error marshaling route lookup config: %v: %v
• rls: json unmarshal failed for service config %+v: %v
• rls: json unmarshal failed for child policy config %q: %v
• rls: json marshal failed for child policy config {%+v}: %v
• xds_wrr_locality: config generated %v is invalid: %v

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/eeae4e1a1dca9459. Report an issue: GitHub.