proxyd: Add batch size metric and configurable max (#3545)

* proxyd: Add batch size metric and configurable max

The max batch size will be overwritten if it is over `MaxBatchRPCCallsHardLimit`.

Builds on https://github.com/ethereum-optimism/optimism/pull/3544.

* changeset

* fix lint

* fix test

.changeset/mean-islands-rush.md

+---
+'@eth-optimism/proxyd': patch
+---
+
+Batch metrics and max batch size

proxyd/config.go

@@ -95,6 +95,11 @@ type BackendGroupsConfig map[string]*BackendGroupConfig
 
 type MethodMappingsConfig map[string]string
 
+type BatchConfig struct {
+	MaxSize      int    `toml:"max_size"`
+	ErrorMessage string `toml:"error_message"`
+}
+
 type Config struct {
 	WSBackendGroup        string              `toml:"ws_backend_group"`
 	Server                ServerConfig        `toml:"server"`
@@ -104,6 +109,7 @@ type Config struct {
 	RateLimit             RateLimitConfig     `toml:"rate_limit"`
 	BackendOptions        BackendOptions      `toml:"backend"`
 	Backends              BackendsConfig      `toml:"backends"`
+	BatchConfig           BatchConfig         `toml:"batch"`
 	Authentication        map[string]string   `toml:"authentication"`
 	BackendGroups         BackendGroupsConfig `toml:"backend_groups"`
 	RPCMethodMappings     map[string]string   `toml:"rpc_method_mappings"`

proxyd/integration_tests/batching_test.go

@@ -33,13 +33,13 @@ func TestBatching(t *testing.T) {
 	callMock1 := mockResult{"eth_call", "1", "ekans1"}
 
 	tests := []struct {
-		name                string
-		handler             http.Handler
-		mocks               []mockResult
-		reqs                []*proxyd.RPCReq
-		expectedRes         string
-		maxBatchSize        int
-		numExpectedForwards int
+		name                 string
+		handler              http.Handler
+		mocks                []mockResult
+		reqs                 []*proxyd.RPCReq
+		expectedRes          string
+		maxUpstreamBatchSize int
+		numExpectedForwards  int
 	}{
 		{
 			name:  "backend returns batches out of order",
@@ -49,9 +49,9 @@ func TestBatching(t *testing.T) {
 				NewRPCReq("2", "eth_chainId", nil),
 				NewRPCReq("3", "eth_chainId", nil),
 			},
-			expectedRes:         asArray(chainIDResponse1, chainIDResponse2, chainIDResponse3),
-			maxBatchSize:        2,
-			numExpectedForwards: 2,
+			expectedRes:          asArray(chainIDResponse1, chainIDResponse2, chainIDResponse3),
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  2,
 		},
 		{
 			// infura behavior
@@ -65,8 +65,8 @@ func TestBatching(t *testing.T) {
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":1,"jsonrpc":"2.0"}`,
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":2,"jsonrpc":"2.0"}`,
 			),
-			maxBatchSize:        10,
-			numExpectedForwards: 1,
+			maxUpstreamBatchSize: 10,
+			numExpectedForwards:  1,
 		},
 		{
 			name:    "backend returns single RPC response object for minibatches",
@@ -79,8 +79,8 @@ func TestBatching(t *testing.T) {
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":1,"jsonrpc":"2.0"}`,
 				`{"error":{"code":-32011,"message":"no backends available for method"},"id":2,"jsonrpc":"2.0"}`,
 			),
-			maxBatchSize:        1,
-			numExpectedForwards: 2,
+			maxUpstreamBatchSize: 1,
+			numExpectedForwards:  2,
 		},
 		{
 			name: "duplicate request ids are on distinct batches",
@@ -96,9 +96,24 @@ func TestBatching(t *testing.T) {
 				NewRPCReq("1", "eth_chainId", nil),
 				NewRPCReq("1", "eth_call", nil),
 			},
-			expectedRes:         asArray(netVersionResponse1, chainIDResponse2, chainIDResponse1, callResponse1),
-			maxBatchSize:        2,
-			numExpectedForwards: 3,
+			expectedRes:          asArray(netVersionResponse1, chainIDResponse2, chainIDResponse1, callResponse1),
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  3,
+		},
+		{
+			name:  "over max size",
+			mocks: []mockResult{},
+			reqs: []*proxyd.RPCReq{
+				NewRPCReq("1", "net_version", nil),
+				NewRPCReq("2", "eth_chainId", nil),
+				NewRPCReq("3", "eth_chainId", nil),
+				NewRPCReq("4", "eth_call", nil),
+				NewRPCReq("5", "eth_call", nil),
+				NewRPCReq("6", "eth_call", nil),
+			},
+			expectedRes:          "{\"error\":{\"code\":-32014,\"message\":\"over batch size custom message\"},\"id\":null,\"jsonrpc\":\"2.0\"}",
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  0,
 		},
 		{
 			name: "eth_accounts does not get forwarded",
@@ -109,15 +124,15 @@ func TestBatching(t *testing.T) {
 				NewRPCReq("1", "eth_call", nil),
 				NewRPCReq("2", "eth_accounts", nil),
 			},
-			expectedRes:         asArray(callResponse1, ethAccountsResponse2),
-			maxBatchSize:        2,
-			numExpectedForwards: 1,
+			expectedRes:          asArray(callResponse1, ethAccountsResponse2),
+			maxUpstreamBatchSize: 2,
+			numExpectedForwards:  1,
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			config.Server.MaxUpstreamBatchSize = tt.maxBatchSize
+			config.Server.MaxUpstreamBatchSize = tt.maxUpstreamBatchSize
 
 			handler := tt.handler
 			if handler == nil {

proxyd/integration_tests/testdata/batching.toml

@@ -17,3 +17,7 @@ backends = ["good"]
 eth_chainId = "main"
 net_version = "main"
 eth_call = "main"
+
+[batch]
+error_message = "over batch size custom message"
+max_size = 5
\ No newline at end of file

proxyd/metrics.go

@@ -222,6 +222,20 @@ var (
 	}, []string{
 		"backend_name",
 	})
+
+	batchSizeHistogram = promauto.NewHistogram(prometheus.HistogramOpts{
+		Namespace: MetricsNamespace,
+		Name:      "batch_size_summary",
+		Help:      "Summary of batch sizes",
+		Buckets: []float64{
+			1,
+			5,
+			10,
+			25,
+			50,
+			100,
+		},
+	})
 )
 
 func RecordRedisError(source string) {
@@ -278,3 +292,7 @@ func RecordCacheHit(method string) {
 func RecordCacheMiss(method string) {
 	cacheMissesTotal.WithLabelValues(method).Inc()
 }
+
+func RecordBatchSize(size int) {
+	batchSizeHistogram.Observe(float64(size))
+}

proxyd/proxyd.go

@@ -65,6 +65,9 @@ func Start(config *Config) (func(), error) {
 	if config.WhitelistErrorMessage != "" {
 		ErrMethodNotWhitelisted.Message = config.WhitelistErrorMessage
 	}
+	if config.BatchConfig.ErrorMessage != "" {
+		ErrTooManyBatchRequests.Message = config.BatchConfig.ErrorMessage
+	}
 
 	maxConcurrentRPCs := config.Server.MaxConcurrentRPCs
 	if maxConcurrentRPCs == 0 {
@@ -236,6 +239,7 @@ func Start(config *Config) (func(), error) {
 		config.RateLimit,
 		config.Server.EnableRequestLog,
 		config.Server.MaxRequestBodyLogLen,
+		config.BatchConfig.MaxSize,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("error creating server: %w", err)

proxyd/server.go

@@ -28,7 +28,7 @@ const (
 	ContextKeyAuth              = "authorization"
 	ContextKeyReqID             = "req_id"
 	ContextKeyXForwardedFor     = "x_forwarded_for"
-	MaxBatchRPCCalls            = 100
+	MaxBatchRPCCallsHardLimit   = 100
 	cacheStatusHdr              = "X-Proxyd-Cache-Status"
 	defaultServerTimeout        = time.Second * 10
 	maxRequestBodyLogLen        = 2000
@@ -48,6 +48,7 @@ type Server struct {
 	authenticatedPaths   map[string]string
 	timeout              time.Duration
 	maxUpstreamBatchSize int
+	maxBatchSize         int
 	upgrader             *websocket.Upgrader
 	mainLim              limiter.Store
 	overrideLims         map[string]limiter.Store
@@ -75,6 +76,7 @@ func NewServer(
 	rateLimitConfig RateLimitConfig,
 	enableRequestLog bool,
 	maxRequestBodyLogLen int,
+	maxBatchSize int,
 ) (*Server, error) {
 	if cache == nil {
 		cache = &NoopRPCCache{}
@@ -92,6 +94,10 @@ func NewServer(
 		maxUpstreamBatchSize = defaultMaxUpstreamBatchSize
 	}
 
+	if maxBatchSize == 0 || maxBatchSize > MaxBatchRPCCallsHardLimit {
+		maxBatchSize = MaxBatchRPCCallsHardLimit
+	}
+
 	var mainLim limiter.Store
 	limExemptOrigins := make(map[string]bool)
 	limExemptUserAgents := make(map[string]bool)
@@ -139,6 +145,7 @@ func NewServer(
 		cache:                cache,
 		enableRequestLog:     enableRequestLog,
 		maxRequestBodyLogLen: maxRequestBodyLogLen,
+		maxBatchSize:         maxBatchSize,
 		upgrader: &websocket.Upgrader{
 			HandshakeTimeout: 5 * time.Second,
 		},
@@ -291,7 +298,9 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
-		if len(reqs) > MaxBatchRPCCalls {
+		RecordBatchSize(len(reqs))
+
+		if len(reqs) > s.maxBatchSize {
 			RecordRPCError(ctx, BackendProxyd, MethodUnknown, ErrTooManyBatchRequests)
 			writeRPCError(ctx, w, nil, ErrTooManyBatchRequests)
 			return