Code review feedback

proxyd/backend.go

@@ -11,6 +11,7 @@ import (
 	"math"
 	"math/rand"
 	"net/http"
+	"slices"
 	"sort"
 	"strconv"
 	"strings"
@@ -21,6 +22,7 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/rpc"
 	"github.com/gorilla/websocket"
+	"github.com/mroth/weightedrand/v2"
 	"github.com/prometheus/client_golang/prometheus"
 	"golang.org/x/sync/semaphore"
 
@@ -695,6 +697,26 @@ type BackendGroup struct {
 	Backends        []*Backend
 	WeightedRouting bool
 	Consensus       *ConsensusPoller
+	weightedChooser *weightedrand.Chooser[*Backend, int]
+}
+
+func NewBackendGroup(name string, backends []*Backend, weightedRouting bool) (*BackendGroup, error) {
+	choices := make([]weightedrand.Choice[*Backend, int], len(backends))
+	for i, backend := range backends {
+		choices[i] = weightedrand.Choice[*Backend, int]{Item: backend, Weight: backend.weight}
+	}
+
+	chooser, err := weightedrand.NewChooser(choices...)
+	if err != nil && weightedRouting {
+		return nil, err
+	}
+
+	return &BackendGroup{
+		Name:            name,
+		Backends:        backends,
+		WeightedRouting: weightedRouting,
+		weightedChooser: chooser,
+	}, nil
 }
 
 func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool) ([]*RPCRes, string, error) {
@@ -702,7 +724,7 @@ func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch
 		return nil, "", nil
 	}
 
-	backends := bg.Backends
+	backends := bg.orderedBackendsForRequest()
 
 	overriddenResponses := make([]*indexedReqRes, 0)
 	rewrittenReqs := make([]*RPCReq, 0, len(rpcReqs))
@@ -710,7 +732,6 @@ func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch
 	if bg.Consensus != nil {
 		// When `consensus_aware` is set to `true`, the backend group acts as a load balancer
 		// serving traffic from any backend that agrees in the consensus group
-		backends = bg.loadBalancedConsensusGroup()
 
 		// We also rewrite block tags to enforce compliance with consensus
 		rctx := RewriteContext{
@@ -750,8 +771,6 @@ func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch
 			}
 		}
 		rpcReqs = rewrittenReqs
-	} else if bg.WeightedRouting {
-		backends = randomizeFirstBackendByWeight(backends)
 	}
 
 	rpcRequestsTotal.Inc()
@@ -819,36 +838,19 @@ func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch
 	return nil, "", ErrNoBackends
 }
 
-func randomizeFirstBackendByWeight(backends []*Backend) []*Backend {
-	if len(backends) <= 1 {
-		return backends
-	}
+func moveBackendToStart(choice *Backend, options []*Backend) []*Backend {
+	result := make([]*Backend, 0, len(options))
 
-	totalWeight := 0
-	for _, backend := range backends {
-		totalWeight += backend.weight
+	if slices.Contains(options, choice) {
+		result = append(result, choice)
 	}
 
-	r := rand.New(rand.NewSource(time.Now().UnixNano()))
-	random := r.Intn(totalWeight)
-	currentSum := 0
-
-	for idx, backend := range backends {
-		currentSum += backend.weight
-		if currentSum > random {
-			return moveIndexToStart(backends, idx)
+	for _, opt := range options {
+		if opt != choice {
+			result = append(result, opt)
 		}
 	}
 
-	log.Warn("unable to select weighted backend, using ordered input")
-	return backends
-}
-
-func moveIndexToStart(backends []*Backend, index int) []*Backend {
-	result := make([]*Backend, 0, len(backends))
-	result = append(result, backends[index])
-	result = append(result, backends[:index]...)
-	result = append(result, backends[index+1:]...)
 	return result
 }
 
@@ -889,6 +891,17 @@ func (bg *BackendGroup) ProxyWS(ctx context.Context, clientConn *websocket.Conn,
 	return nil, ErrNoBackends
 }
 
+func (bg *BackendGroup) orderedBackendsForRequest() []*Backend {
+	backends := bg.Backends
+	if bg.Consensus != nil {
+		backends = bg.loadBalancedConsensusGroup()
+	} else if bg.WeightedRouting {
+		choice := bg.weightedChooser.Pick()
+		backends = moveBackendToStart(choice, backends)
+	}
+	return backends
+}
+
 func (bg *BackendGroup) loadBalancedConsensusGroup() []*Backend {
 	cg := bg.Consensus.GetConsensusGroup()
 
@@ -917,8 +930,9 @@ func (bg *BackendGroup) loadBalancedConsensusGroup() []*Backend {
 	})
 
 	if bg.WeightedRouting {
-		backendsHealthy = randomizeFirstBackendByWeight(backendsHealthy)
-		backendsDegraded = randomizeFirstBackendByWeight(backendsDegraded)
+		choice := bg.weightedChooser.Pick()
+		backendsHealthy = moveBackendToStart(choice, backendsHealthy)
+		backendsDegraded = moveBackendToStart(choice, backendsDegraded)
 	}
 
 	// healthy are put into a priority position

proxyd/backend_test.go

@@ -2,6 +2,7 @@ package proxyd
 
 import (
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"testing"
 )
 
@@ -20,51 +21,116 @@ func TestStripXFF(t *testing.T) {
 	}
 }
 
-func TestMoveIndexToStart(t *testing.T) {
-	backends := []*Backend{
+func TestCreateBackendGroup(t *testing.T) {
+	unweightedOne := &Backend{
+		Name:   "one",
+		weight: 0,
+	}
+
+	unweightedTwo := &Backend{
+		Name:   "two",
+		weight: 0,
+	}
+
+	weightedOne := &Backend{
+		Name:   "one",
+		weight: 1,
+	}
+
+	weightedTwo := &Backend{
+		Name:   "two",
+		weight: 1,
+	}
+
+	tests := []struct {
+		name            string
+		backends        []*Backend
+		weightedRouting bool
+		expectError     bool
+	}{
 		{
-			Name: "node1",
+			name:            "weighting disabled",
+			backends:        []*Backend{unweightedOne, unweightedTwo},
+			weightedRouting: false,
+			expectError:     false,
 		},
 		{
-			Name: "node1",
+			name:            "weighting enabled -- all nodes have weight",
+			backends:        []*Backend{weightedOne, weightedTwo},
+			weightedRouting: true,
+			expectError:     false,
 		},
 		{
-			Name: "node1",
+			name:            "weighting enabled -- some nodes have weight",
+			backends:        []*Backend{weightedOne, unweightedTwo},
+			weightedRouting: true,
+			expectError:     false,
 		},
+		{
+			name:            "weighting enabled -- no nodes have weight",
+			backends:        []*Backend{unweightedOne, unweightedTwo},
+			weightedRouting: true,
+			expectError:     true,
+		},
+	}
+
+	for _, test := range tests {
+		result, err := NewBackendGroup(test.name, test.backends, test.weightedRouting)
+
+		if test.expectError {
+			require.Error(t, err)
+		} else {
+			require.NoError(t, err)
+			assert.Equal(t, test.name, result.Name)
+			assert.Equal(t, test.backends, test.backends)
+			assert.Equal(t, test.weightedRouting, test.weightedRouting)
+		}
+	}
+
+}
+
+func TestMoveIndexToStart(t *testing.T) {
+	one := &Backend{
+		Name: "one",
+	}
+
+	two := &Backend{
+		Name: "two",
+	}
+
+	three := &Backend{
+		Name: "three",
 	}
 
 	tests := []struct {
-		index int
-		out   []*Backend
+		choice *Backend
+		input  []*Backend
+		output []*Backend
 	}{
 		{
-			index: 0,
-			out: []*Backend{
-				backends[0],
-				backends[1],
-				backends[2],
-			},
+			choice: one,
+			input:  []*Backend{one, two, three},
+			output: []*Backend{one, two, three},
+		},
+		{
+			choice: two,
+			input:  []*Backend{one, two, three},
+			output: []*Backend{two, one, three},
 		},
 		{
-			index: 1,
-			out: []*Backend{
-				backends[1],
-				backends[0],
-				backends[2],
-			},
+			choice: three,
+			input:  []*Backend{one, two},
+			output: []*Backend{one, two},
 		},
 		{
-			index: 2,
-			out: []*Backend{
-				backends[2],
-				backends[0],
-				backends[1],
-			},
+			choice: one,
+			input:  []*Backend{one},
+			output: []*Backend{one},
 		},
 	}
 
 	for _, test := range tests {
-		result := moveIndexToStart(backends, test.index)
-		assert.Equal(t, test.out, result)
+		result := moveBackendToStart(test.choice, test.input)
+		assert.Equal(t, test.output, result)
 	}
 }

proxyd/go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/gorilla/mux v1.8.0
 	github.com/gorilla/websocket v1.5.0
 	github.com/hashicorp/golang-lru v1.0.2
+	github.com/mroth/weightedrand/v2 v2.1.0
 	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.17.0
 	github.com/redis/go-redis/v9 v9.2.1

proxyd/go.sum

@@ -143,6 +143,8 @@ github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0/go.mod h1:QUyp042oQth
 github.com/mmcloughlin/addchain v0.4.0 h1:SobOdjm2xLj1KkXN5/n0xTIWyZA2+s99UCY1iPfkHRY=
 github.com/mmcloughlin/addchain v0.4.0/go.mod h1:A86O+tHqZLMNO4w6ZZ4FlVQEadcoqkyU72HC5wJ4RlU=
 github.com/mmcloughlin/profile v0.1.1/go.mod h1:IhHD7q1ooxgwTgjxQYkACGA77oFTDdFVejUS1/tS/qU=
+github.com/mroth/weightedrand/v2 v2.1.0 h1:o1ascnB1CIVzsqlfArQQjeMy1U0NcIbBO5rfd5E/OeU=
+github.com/mroth/weightedrand/v2 v2.1.0/go.mod h1:f2faGsfOGOwc1p94wzHKKZyTpcJUW7OJ/9U4yfiNAOU=
 github.com/nxadm/tail v1.4.4 h1:DQuhQpB1tVlglWS2hLQ5OV6B5r8aGxSrPc5Qo6uTN78=
 github.com/nxadm/tail v1.4.4/go.mod h1:kenIhsEOeOJmVchQTgglprH7qJGnHDVpk1VPCcaMI8A=
 github.com/olekukonko/tablewriter v0.0.5 h1:P2Ga83D34wi1o9J6Wh1mRuqd4mF/x/lgBS7N7AbDhec=

proxyd/proxyd.go

@@ -175,11 +175,12 @@ func Start(config *Config) (*Server, func(), error) {
 			}
 			backends = append(backends, backendsByName[bName])
 		}
-		group := &BackendGroup{
-			Name:            bgName,
-			WeightedRouting: bg.WeightedRouting,
-			Backends:        backends,
+
+		group, err := NewBackendGroup(bgName, backends, bg.WeightedRouting)
+		if err != nil {
+			return nil, nil, fmt.Errorf("error creating backend group %s: %w", bgName, err)
 		}
+
 		backendGroups[bgName] = group
 	}