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RandomChoice 2 policy wasn't random when the number of targets is 2 (with equal weight) #14028

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merged 2 commits into from
May 30, 2023
Merged

RandomChoice 2 policy wasn't random when the number of targets is 2 (with equal weight) #14028

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65cd130
RandomChoice 2 policy wasn't random when the number of targets is 2
dprotaso May 29, 2023
b4fb149
fix linting
dprotaso May 30, 2023
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5 changes: 5 additions & 0 deletions pkg/activator/net/lb_policy.go
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,11 @@ func randomChoice2Policy(_ context.Context, targets []*podTracker) (func(), *pod
// so fine.
if pick.getWeight() > alt.getWeight() {
pick = alt
} else if pick.getWeight() == alt.getWeight() {
//nolint:gosec // We don't need cryptographic randomness here.
if rand.Int63()%2 == 0 {
pick = alt
}
}
pick.increaseWeight()
return pick.decreaseWeight, pick
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26 changes: 26 additions & 0 deletions pkg/activator/net/lb_policy_test.go
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Expand Up @@ -25,6 +25,32 @@ import (
"knative.dev/serving/pkg/queue"
)

func TestRandomChoice_TwoTrackersDistribution(t *testing.T) {
podTrackers := makeTrackers(2, 0)
counts := map[string]int{}

total := 100
for i := 0; i < total; i++ {
cb, pt := randomChoice2Policy(context.Background(), podTrackers)
cb()
counts[pt.dest]++
}

first := counts[podTrackers[0].dest]
second := counts[podTrackers[1].dest]

// probability of this occurring is 0.5^100
if first == 0 {
t.Error("expected the first tracker to get some requests")
}
if second == 0 {
t.Error("expected the second tracker to get some requests")
}
if first+second != total {
t.Error("expected total requests to equal 100 - was ", first+second)
}
}

func TestRandomChoice2(t *testing.T) {
t.Run("1 tracker", func(t *testing.T) {
podTrackers := makeTrackers(1, 0)
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