max_ring_size value of %d is greater than max supported valu

Error message

max_ring_size value of %d is greater than max supported value %d for this field

What it means

Returned by ringhash.parseConfig (config.go:45-47) when MaxRingSize exceeds ringHashSizeUpperBound (8M). Same memory-cap rationale as MinRingSize. The %d values are the offending value and the 8M bound.

Source

Thrown at balancer/ringhash/config.go:46

	iringhash "google.golang.org/grpc/internal/ringhash"
)

const (
	defaultMinSize         = 1024
	defaultMaxSize         = 4096
	ringHashSizeUpperBound = 8 * 1024 * 1024 // 8M
)

func parseConfig(c json.RawMessage) (*iringhash.LBConfig, error) {
	var cfg iringhash.LBConfig
	if err := json.Unmarshal(c, &cfg); err != nil {
		return nil, err
	}
	if cfg.MinRingSize > ringHashSizeUpperBound {
		return nil, fmt.Errorf("min_ring_size value of %d is greater than max supported value %d for this field", cfg.MinRingSize, ringHashSizeUpperBound)
	}
	if cfg.MaxRingSize > ringHashSizeUpperBound {
		return nil, fmt.Errorf("max_ring_size value of %d is greater than max supported value %d for this field", cfg.MaxRingSize, ringHashSizeUpperBound)
	}
	if cfg.MinRingSize == 0 {
		cfg.MinRingSize = defaultMinSize
	}
	if cfg.MaxRingSize == 0 {
		cfg.MaxRingSize = defaultMaxSize
	}
	if cfg.MinRingSize > cfg.MaxRingSize {
		return nil, fmt.Errorf("min %v is greater than max %v", cfg.MinRingSize, cfg.MaxRingSize)
	}
	if cfg.MinRingSize > envconfig.RingHashCap {
		cfg.MinRingSize = envconfig.RingHashCap
	}
	if cfg.MaxRingSize > envconfig.RingHashCap {
		cfg.MaxRingSize = envconfig.RingHashCap
	}
	if !envconfig.RingHashSetRequestHashKey {
		cfg.RequestHashHeader = ""

View on GitHub (pinned to 03255a9237)

Solutions

Set maxRingSize to at most 8388608; default is 4096 and rarely needs to be larger.
Verify the xDS Cluster.ringHashLbConfig.maximumRingSize value in the control plane.

Example fix

// before
raw := `{"minRingSize": 1024, "maxRingSize": 100000000}` // > 8M -> error

// after
raw := `{"minRingSize": 1024, "maxRingSize": 4096}`

Defensive patterns

Strategy: validation

Validate before calling

const ringHashUpperBound = 8 * 1024 * 1024
func validateMaxRingSize(raw []byte) error {
    var c struct{ MaxRingSize uint64 `json:"maxRingSize"` }
    _ = json.Unmarshal(raw, &c)
    if c.MaxRingSize > ringHashUpperBound {
        return fmt.Errorf("maxRingSize %d > %d", c.MaxRingSize, ringHashUpperBound)
    }
    return nil
}

Prevention

Same as minRingSize: small thousands are plenty.
Lint the config in CI to reject values above the 8M cap.

When it happens

Trigger: The ring_hash config sets maxRingSize above 8388608.

Common situations: Unit confusion (treating the field as bytes), xDS control-plane misconfiguration, or attempting to maximize distribution without realizing the hard cap.

Related errors

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/7bae25ac94fe7435. Report an issue: GitHub.