Merge pull request #37 from buildkite/dont-scale-out-over-max

Avoid scale out over max and scale in under min
buildkite · Oct 19, 2020 · 456bf3b · 456bf3b
2 parents 12d9dfb + 3cab033
commit 456bf3b
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diff --git a/scaler/scaler.go b/scaler/scaler.go
@@ -170,6 +170,11 @@ func (s *Scaler) scaleIn(desired int64, current AutoscaleGroupDetails) error {
 		}
 
 		desired = current.DesiredCount + factoredChange
+
+		if desired < current.MinSize {
+			log.Printf("⚠️  Post scalein-factor desired count lower than MinSize, capping at %d", current.MinSize)
+			desired = current.MinSize
+		}
 	}
 
 	// Correct negative values if we get them
@@ -222,6 +227,11 @@ func (s *Scaler) scaleOut(desired int64, current AutoscaleGroupDetails) error {
 		}
 
 		desired = current.DesiredCount + factoredChange
+
+		if desired > current.MaxSize {
+			log.Printf("⚠️  Post scaleout-factor desired count exceed MaxSize, capping at %d", current.MaxSize)
+			desired = current.MaxSize
+		}
 	}
 
 	log.Printf("Scaling OUT 📈 to %d instances (currently %d)", desired, current.DesiredCount)

diff --git a/scaler/scaler_test.go b/scaler/scaler_test.go
@@ -111,6 +111,19 @@ func TestScalingOutWithoutError(t *testing.T) {
 			currentDesiredCapacity:  11,
 			expectedDesiredCapacity: 12,
 		},
+		// Scale-out with a factor too large
+		{
+			metrics: buildkite.AgentMetrics{
+				ScheduledJobs: 10,
+			},
+			params: Params{
+				AgentsPerInstance: 1,
+				ScaleOutParams: ScaleParams{
+					Factor: 500.0,
+				},
+			},
+			expectedDesiredCapacity: 100.0,
+		},
 		// Cool-down period is enforced
 		{
 			metrics: buildkite.AgentMetrics{