Configurable Load Balancing

go.mod

@@ -28,7 +28,7 @@ require (
 	golang.org/x/sys v0.36.0
 	golang.org/x/time v0.10.0
 	google.golang.org/api v0.198.0
-	google.golang.org/grpc v1.74.2
+	google.golang.org/grpc v1.75.0
 	gopkg.in/yaml.v3 v3.0.1
 	k8s.io/api v0.33.4
 	k8s.io/apiextensions-apiserver v0.33.4
@@ -153,8 +153,8 @@ require (
 	golang.org/x/text v0.29.0 // indirect
 	golang.org/x/tools v0.37.0 // indirect
 	gomodules.xyz/jsonpatch/v2 v2.5.0 // indirect
-	google.golang.org/genproto/googleapis/api v0.0.0-20250603155806-513f23925822 // indirect
-	google.golang.org/genproto/googleapis/rpc v0.0.0-20250603155806-513f23925822 // indirect
+	google.golang.org/genproto/googleapis/api v0.0.0-20250707201910-8d1bb00bc6a7 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20250818200422-3122310a409c // indirect
 	google.golang.org/protobuf v1.36.8 // indirect
 	gopkg.in/evanphx/json-patch.v4 v4.12.0 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect

go.sum

@@ -507,8 +507,9 @@ golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8T
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 gomodules.xyz/jsonpatch/v2 v2.5.0 h1:JELs8RLM12qJGXU4u/TO3V25KW8GreMKl9pdkk14RM0=
 gomodules.xyz/jsonpatch/v2 v2.5.0/go.mod h1:AH3dM2RI6uoBZxn3LVrfvJ3E0/9dG4cSrbuBJT4moAY=
-gonum.org/v1/gonum v0.0.0-20181121035319-3f7ecaa7e8ca h1:PupagGYwj8+I4ubCxcmcBRk3VlUWtTg5huQpZR9flmE=
 gonum.org/v1/gonum v0.0.0-20181121035319-3f7ecaa7e8ca/go.mod h1:Y+Yx5eoAFn32cQvJDxZx5Dpnq+c3wtXuadVZAcxbbBo=
+gonum.org/v1/gonum v0.16.0 h1:5+ul4Swaf3ESvrOnidPp4GZbzf0mxVQpDCYUQE7OJfk=
+gonum.org/v1/gonum v0.16.0/go.mod h1:fef3am4MQ93R2HHpKnLk4/Tbh/s0+wqD5nfa6Pnwy4E=
 gonum.org/v1/netlib v0.0.0-20181029234149-ec6d1f5cefe6/go.mod h1:wa6Ws7BG/ESfp6dHfk7C6KdzKA7wR7u/rKwOGE66zvw=
 google.golang.org/api v0.198.0 h1:OOH5fZatk57iN0A7tjJQzt6aPfYQ1JiWkt1yGseazks=
 google.golang.org/api v0.198.0/go.mod h1:/Lblzl3/Xqqk9hw/yS97TImKTUwnf1bv89v7+OagJzc=
@@ -517,17 +518,17 @@ google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
 google.golang.org/genproto v0.0.0-20190819201941-24fa4b261c55/go.mod h1:DMBHOl98Agz4BDEuKkezgsaosCRResVns1a3J2ZsMNc=
 google.golang.org/genproto v0.0.0-20200526211855-cb27e3aa2013/go.mod h1:NbSheEEYHJ7i3ixzK3sjbqSGDJWnxyFXZblF3eUsNvo=
-google.golang.org/genproto/googleapis/api v0.0.0-20250603155806-513f23925822 h1:oWVWY3NzT7KJppx2UKhKmzPq4SRe0LdCijVRwvGeikY=
-google.golang.org/genproto/googleapis/api v0.0.0-20250603155806-513f23925822/go.mod h1:h3c4v36UTKzUiuaOKQ6gr3S+0hovBtUrXzTG/i3+XEc=
-google.golang.org/genproto/googleapis/rpc v0.0.0-20250603155806-513f23925822 h1:fc6jSaCT0vBduLYZHYrBBNY4dsWuvgyff9noRNDdBeE=
-google.golang.org/genproto/googleapis/rpc v0.0.0-20250603155806-513f23925822/go.mod h1:qQ0YXyHHx3XkvlzUtpXDkS29lDSafHMZBAZDc03LQ3A=
+google.golang.org/genproto/googleapis/api v0.0.0-20250707201910-8d1bb00bc6a7 h1:FiusG7LWj+4byqhbvmB+Q93B/mOxJLN2DTozDuZm4EU=
+google.golang.org/genproto/googleapis/api v0.0.0-20250707201910-8d1bb00bc6a7/go.mod h1:kXqgZtrWaf6qS3jZOCnCH7WYfrvFjkC51bM8fz3RsCA=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20250818200422-3122310a409c h1:qXWI/sQtv5UKboZ/zUk7h+mrf/lXORyI+n9DKDAusdg=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20250818200422-3122310a409c/go.mod h1:gw1tLEfykwDz2ET4a12jcXt4couGAm7IwsVaTy0Sflo=
 google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
 google.golang.org/grpc v1.23.0/go.mod h1:Y5yQAOtifL1yxbo5wqy6BxZv8vAUGQwXBOALyacEbxg=
 google.golang.org/grpc v1.25.1/go.mod h1:c3i+UQWmh7LiEpx4sFZnkU36qjEYZ0imhYfXVyQciAY=
 google.golang.org/grpc v1.27.0/go.mod h1:qbnxyOmOxrQa7FizSgH+ReBfzJrCY1pSN7KXBS8abTk=
 google.golang.org/grpc v1.33.2/go.mod h1:JMHMWHQWaTccqQQlmk3MJZS+GWXOdAesneDmEnv2fbc=
-google.golang.org/grpc v1.74.2 h1:WoosgB65DlWVC9FqI82dGsZhWFNBSLjQ84bjROOpMu4=
-google.golang.org/grpc v1.74.2/go.mod h1:CtQ+BGjaAIXHs/5YS3i473GqwBBa1zGQNevxdeBEXrM=
+google.golang.org/grpc v1.75.0 h1:+TW+dqTd2Biwe6KKfhE5JpiYIBWq865PhKGSXiivqt4=
+google.golang.org/grpc v1.75.0/go.mod h1:JtPAzKiq4v1xcAB2hydNlWI2RnF85XXcV0mhKXr2ecQ=
 google.golang.org/protobuf v0.0.0-20200109180630-ec00e32a8dfd/go.mod h1:DFci5gLYBciE7Vtevhsrf46CRTquxDuWsQurQQe4oz8=
 google.golang.org/protobuf v0.0.0-20200221191635-4d8936d0db64/go.mod h1:kwYJMbMJ01Woi6D6+Kah6886xMZcty6N08ah7+eCXa0=
 google.golang.org/protobuf v0.0.0-20200228230310-ab0ca4ff8a60/go.mod h1:cfTl7dwQJ+fmap5saPgwCLgHXTUD7jkjRqWcaiX5VyM=

pkg/activator/net/lb_policy.go

@@ -21,6 +21,7 @@ package net
 import (
 	"context"
 	"math/rand"
+	"sort"
 	"sync"
 )
 
@@ -31,27 +32,61 @@ import (
 // and pointers therein are immutable.
 type lbPolicy func(ctx context.Context, targets []*podTracker) (func(), *podTracker)
 
+type TrackerLoad struct {
+	tracker  *podTracker
+	inFlight uint64
+}
+
 // randomLBPolicy is a load balancer policy that picks a random target.
 // This approximates the LB policy done by K8s Service (IPTables based).
 func randomLBPolicy(_ context.Context, targets []*podTracker) (func(), *podTracker) {
-	return noop, targets[rand.Intn(len(targets))] //nolint:gosec
+	if len(targets) == 0 {
+		return noop, nil
+	}
+
+	// Filter out nil trackers to ensure uniform distribution
+	validTargets := make([]*podTracker, 0, len(targets))
+	for _, t := range targets {
+		if t != nil {
+			validTargets = append(validTargets, t)
+		}
+	}
+
+	if len(validTargets) == 0 {
+		return noop, nil
+	}
+
+	return noop, validTargets[rand.Intn(len(validTargets))] //nolint:gosec
 }
 
 // randomChoice2Policy implements the Power of 2 choices LB algorithm
 func randomChoice2Policy(_ context.Context, targets []*podTracker) (func(), *podTracker) {
-	// Avoid random if possible.
-	l := len(targets)
+	// Filter out nil trackers first to ensure uniform distribution
+	validTargets := make([]*podTracker, 0, len(targets))
+	for _, t := range targets {
+		if t != nil {
+			validTargets = append(validTargets, t)
+		}
+	}
+
+	l := len(validTargets)
+	if l == 0 {
+		return noop, nil
+	}
+
 	// One tracker = no choice.
 	if l == 1 {
-		pick := targets[0]
+		pick := validTargets[0]
 		pick.increaseWeight()
 		return pick.decreaseWeight, pick
 	}
-	r1, r2 := 0, 1
+
 	// Two trackers - we know both contestants,
 	// otherwise pick 2 random unequal integers.
+	r1, r2 := 0, 1
 	if l > 2 {
-		r1, r2 = rand.Intn(l), rand.Intn(l-1) //nolint:gosec // We don't need cryptographic randomness here.
+		r1 = rand.Intn(l)     //nolint:gosec // We don't need cryptographic randomness for load balancing
+		r2 = rand.Intn(l - 1) //nolint:gosec // We don't need cryptographic randomness here.
 		// shift second half of second rand.Intn down so we're picking
 		// from range of numbers other than r1.
 		// i.e. rand.Intn(l-1) range is now from range [0,r1),[r1+1,l).
@@ -60,7 +95,8 @@ func randomChoice2Policy(_ context.Context, targets []*podTracker) (func(), *pod
 		}
 	}
 
-	pick, alt := targets[r1], targets[r2]
+	pick, alt := validTargets[r1], validTargets[r2]
+
 	// Possible race here, but this policy is for CC=0,
 	// so fine.
 	if pick.getWeight() > alt.getWeight() {
@@ -75,17 +111,22 @@ func randomChoice2Policy(_ context.Context, targets []*podTracker) (func(), *pod
 	return pick.decreaseWeight, pick
 }
 
-// firstAvailableLBPolicy is a load balancer policy, that picks the first target
+// firstAvailableLBPolicy is a load balancer policy that picks the first target
 // that has capacity to serve the request right now.
 func firstAvailableLBPolicy(ctx context.Context, targets []*podTracker) (func(), *podTracker) {
 	for _, t := range targets {
-		if cb, ok := t.Reserve(ctx); ok {
-			return cb, t
+		if t != nil {
+			if cb, ok := t.Reserve(ctx); ok {
+				return cb, t
+			}
 		}
 	}
 	return noop, nil
 }
 
+// roundRobinPolicy is a load balancer policy that tries all targets in order until one responds,
+// using it as the target. It then continues in order from the last target to determine
+// subsequent targets
 func newRoundRobinPolicy() lbPolicy {
 	var (
 		mu  sync.Mutex
@@ -104,13 +145,50 @@ func newRoundRobinPolicy() lbPolicy {
 		// round robin fashion.
 		for i := range l {
 			p := (idx + i) % l
-			if cb, ok := targets[p].Reserve(ctx); ok {
-				// We want to start with the next index.
-				idx = p + 1
-				return cb, targets[p]
+			if targets[p] != nil {
+				if cb, ok := targets[p].Reserve(ctx); ok {
+					// We want to start with the next index.
+					idx = p + 1
+					return cb, targets[p]
+				}
 			}
 		}
 		// We exhausted all the options...
 		return noop, nil
 	}
 }
+
+// leastConnectionsPolicy is a load balancer policy that uses the tracker with the
+// least connections to determine the next target
+func leastConnectionsPolicy(ctx context.Context, targets []*podTracker) (func(), *podTracker) {
+	trackerLoads := make([]TrackerLoad, len(targets))
+	for i, t := range targets {
+		if t != nil {
+			// Use the weight field as a proxy for in-flight connections
+			weight := t.weight.Load()
+			if weight < 0 {
+				weight = 0
+			}
+			// Safe conversion: weight is guaranteed to be non-negative after the check above
+			// Since weight is int32 and non-negative, it will always fit in uint64
+			// Use explicit check for gosec G115
+			var inFlight uint64
+			if weight >= 0 {
+				inFlight = uint64(weight)
+			}
+			trackerLoads[i] = TrackerLoad{tracker: t, inFlight: inFlight}
+		}
+	}
+	sort.Slice(trackerLoads, func(i, j int) bool {
+		return trackerLoads[i].inFlight < trackerLoads[j].inFlight
+	})
+	for _, tl := range trackerLoads {
+		if tl.tracker == nil {
+			continue
+		}
+		if cb, ok := tl.tracker.Reserve(ctx); ok {
+			return cb, tl.tracker
+		}
+	}
+	return noop, nil
+}