proxyd: add weighting feature to node selection

proxyd/proxyd/backend.go

@@ -159,6 +159,8 @@ type Backend struct {
 	latencySlidingWindow         *sw.AvgSlidingWindow
 	networkRequestsSlidingWindow *sw.AvgSlidingWindow
 	networkErrorsSlidingWindow   *sw.AvgSlidingWindow
+
+	weight int
 }
 
 type BackendOpt func(b *Backend)
@@ -239,6 +241,12 @@ func WithConsensusForcedCandidate(forcedCandidate bool) BackendOpt {
 	}
 }
 
+func WithWeight(weight int) BackendOpt {
+	return func(b *Backend) {
+		b.weight = weight
+	}
+}
+
 func WithMaxDegradedLatencyThreshold(maxDegradedLatencyThreshold time.Duration) BackendOpt {
 	return func(b *Backend) {
 		b.maxDegradedLatencyThreshold = maxDegradedLatencyThreshold
@@ -685,6 +693,7 @@ func sortBatchRPCResponse(req []*RPCReq, res []*RPCRes) {
 type BackendGroup struct {
 	Name               string
 	Backends           []*Backend
+	UseWeightedRouting bool
 	Consensus          *ConsensusPoller
 }
 
@@ -741,6 +750,8 @@ func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch
 			}
 		}
 		rpcReqs = rewrittenReqs
+	} else if bg.UseWeightedRouting {
+		backends = randomizeFirstBackendByWeight(backends)
 	}
 
 	rpcRequestsTotal.Inc()
@@ -808,6 +819,39 @@ func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch
 	return nil, "", ErrNoBackends
 }
 
+func randomizeFirstBackendByWeight(backends []*Backend) []*Backend {
+	if len(backends) == 0 {
+		return backends
+	}
+
+	totalWeight := 0
+	for _, backend := range backends {
+		totalWeight += backend.weight
+	}
+
+	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)
+		}
+	}
+
+	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
+}
+
 func (bg *BackendGroup) ProxyWS(ctx context.Context, clientConn *websocket.Conn, methodWhitelist *StringSet) (*WSProxier, error) {
 	for _, back := range bg.Backends {
 		proxier, err := back.ProxyWS(clientConn, methodWhitelist)
@@ -872,6 +916,11 @@ func (bg *BackendGroup) loadBalancedConsensusGroup() []*Backend {
 		backendsDegraded[i], backendsDegraded[j] = backendsDegraded[j], backendsDegraded[i]
 	})
 
+	if bg.UseWeightedRouting {
+		backendsHealthy = randomizeFirstBackendByWeight(backendsHealthy)
+		backendsDegraded = randomizeFirstBackendByWeight(backendsDegraded)
+	}
+
 	// healthy are put into a priority position
 	// degraded backends are used as fallback
 	backendsHealthy = append(backendsHealthy, backendsDegraded...)

proxyd/proxyd/backend_test.go

@@ -19,3 +19,52 @@ func TestStripXFF(t *testing.T) {
 		assert.Equal(t, test.out, actual)
 	}
 }
+
+func TestMoveIndexToStart(t *testing.T) {
+	backends := []*Backend{
+		{
+			Name: "node1",
+		},
+		{
+			Name: "node1",
+		},
+		{
+			Name: "node1",
+		},
+	}
+
+	tests := []struct {
+		index int
+		out   []*Backend
+	}{
+		{
+			index: 0,
+			out: []*Backend{
+				backends[0],
+				backends[1],
+				backends[2],
+			},
+		},
+		{
+			index: 1,
+			out: []*Backend{
+				backends[1],
+				backends[0],
+				backends[2],
+			},
+		},
+		{
+			index: 2,
+			out: []*Backend{
+				backends[2],
+				backends[0],
+				backends[1],
+			},
+		},
+	}
+
+	for _, test := range tests {
+		result := moveIndexToStart(backends, test.index)
+		assert.Equal(t, test.out, result)
+	}
+}

proxyd/proxyd/config.go

@@ -98,6 +98,8 @@ type BackendConfig struct {
 	ConsensusSkipPeerCountCheck bool   `toml:"consensus_skip_peer_count"`
 	ConsensusForcedCandidate    bool   `toml:"consensus_forced_candidate"`
 	ConsensusReceiptsTarget     string `toml:"consensus_receipts_target"`
+
+	Weight int `toml:"weight"`
 }
 
 type BackendsConfig map[string]*BackendConfig
@@ -105,6 +107,8 @@ type BackendsConfig map[string]*BackendConfig
 type BackendGroupConfig struct {
 	Backends []string `toml:"backends"`
 
+	UseWeightedRouting bool `toml:"weighted_routing"`
+
 	ConsensusAware        bool   `toml:"consensus_aware"`
 	ConsensusAsyncHandler string `toml:"consensus_handler"`
 

proxyd/proxyd/proxyd.go

@@ -144,6 +144,7 @@ func Start(config *Config) (*Server, func(), error) {
 		opts = append(opts, WithProxydIP(os.Getenv("PROXYD_IP")))
 		opts = append(opts, WithConsensusSkipPeerCountCheck(cfg.ConsensusSkipPeerCountCheck))
 		opts = append(opts, WithConsensusForcedCandidate(cfg.ConsensusForcedCandidate))
+		opts = append(opts, WithWeight(cfg.Weight))
 
 		receiptsTarget, err := ReadFromEnvOrConfig(cfg.ConsensusReceiptsTarget)
 		if err != nil {
@@ -176,6 +177,7 @@ func Start(config *Config) (*Server, func(), error) {
 		}
 		group := &BackendGroup{
 			Name:               bgName,
+			UseWeightedRouting: bg.UseWeightedRouting,
 			Backends:           backends,
 		}
 		backendGroups[bgName] = group