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fix(collector): respect HPA scale; don't cap replicas at minReplicas #4401

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fix(collector): respect HPA scale; don't cap replicas at minReplicas #4401

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6 changes: 6 additions & 0 deletions .chloggen/bugfix-autoscaler-replicas-respect-spec.yaml
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
change_type: bug_fix
component: collector
note: "Fix autoscaler not scaling above minReplicas; replicas now respect the scale subresource and never fall below autoscaler.minReplicas."
issues: [4400]
subtext: |
Also rename helper `GetInitialReplicas` to `GetDesiredReplicas` to reflect reconcile-time behavior.
2 changes: 1 addition & 1 deletion internal/manifests/collector/deployment.go
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Expand Up @@ -35,7 +35,7 @@ func Deployment(params manifests.Params) (*appsv1.Deployment, error) {
Annotations: annotations,
},
Spec: appsv1.DeploymentSpec{
Replicas: manifestutils.GetInitialReplicas(params.OtelCol),
Replicas: manifestutils.GetDesiredReplicas(params.OtelCol),
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I believe if GetDesiredReplicas will produce the same effect as described on #2585

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One idea would be adding a condition about the HPA here

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Thank you so much for your comment! I tried reproducing the behavior described in the original issue, but from what I can see, even when we change minReplicas, the Operator doesn’t seem to create a new ReplicaSet, and the Pods aren’t restarted. Could you let me know if I’m missing something here?

apiVersion: opentelemetry.io/v1beta1
kind: OpenTelemetryCollector
metadata:
  name: simplest
spec:
  autoscaler:
    minReplicas: 2
    maxReplicas: 4
  config:
    receivers:
      otlp:
        protocols:
          grpc:
            endpoint: 0.0.0.0:4317
          http:
            endpoint: 0.0.0.0:4318
    processors:
      memory_limiter:
        check_interval: 1s
        limit_percentage: 75
        spike_limit_percentage: 15
      batch:
        send_batch_size: 10000
        timeout: 10s

    exporters:
      debug: {}

    service:
      pipelines:
        traces:
          receivers: [otlp]
          processors: [memory_limiter, batch]
          exporters: [debug]


NAME                                 READY   STATUS    RESTARTS   AGE
simplest-collector-c9fb74dcd-njqd8   1/1     Running   0          28s
simplest-collector-c9fb74dcd-plvd8   1/1     Running   0          28s

Update the minReplicas from 2 to 3.

spec:
  autoscaler:
    minReplicas: 3
    maxReplicas: 4

Add one Pod without restarting the others.

NAME                                 READY   STATUS    RESTARTS   AGE
simplest-collector-c9fb74dcd-6rt44   1/1     Running   0          6s
simplest-collector-c9fb74dcd-njqd8   1/1     Running   0          52s
simplest-collector-c9fb74dcd-plvd8   1/1     Running   0          52s

Selector: &metav1.LabelSelector{
MatchLabels: manifestutils.SelectorLabels(params.OtelCol.ObjectMeta, ComponentOpenTelemetryCollector),
},
Expand Down
19 changes: 17 additions & 2 deletions internal/manifests/collector/deployment_test.go
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Expand Up @@ -728,7 +728,7 @@ func TestDeploymentDNSConfig(t *testing.T) {
assert.Equal(t, d.Spec.Template.Spec.DNSConfig.Nameservers, []string{"8.8.8.8"})
}

func TestGetInitialReplicas(t *testing.T) {
func TestGetDesiredReplicas(t *testing.T) {
tests := []struct {
name string
otelCol v1beta1.OpenTelemetryCollector
Expand Down Expand Up @@ -790,11 +790,26 @@ func TestGetInitialReplicas(t *testing.T) {
},
expected: int32Ptr(6),
},
{
name: "autoscaler-with-minReplicas-spec-replicas-greater",
otelCol: v1beta1.OpenTelemetryCollector{
Spec: v1beta1.OpenTelemetryCollectorSpec{
OpenTelemetryCommonFields: v1beta1.OpenTelemetryCommonFields{
Replicas: int32Ptr(5),
},
Autoscaler: &v1beta1.AutoscalerSpec{
MinReplicas: int32Ptr(3),
MaxReplicas: int32Ptr(10),
},
},
},
expected: int32Ptr(5),
},
}

for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
result := manifestutils.GetInitialReplicas(tt.otelCol)
result := manifestutils.GetDesiredReplicas(tt.otelCol)
if tt.expected == nil {
assert.Nil(t, result)
} else {
Expand Down
2 changes: 1 addition & 1 deletion internal/manifests/collector/statefulset.go
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Expand Up @@ -68,7 +68,7 @@ func StatefulSet(params manifests.Params) (*appsv1.StatefulSet, error) {
TerminationGracePeriodSeconds: params.OtelCol.Spec.TerminationGracePeriodSeconds,
},
},
Replicas: manifestutils.GetInitialReplicas(params.OtelCol),
Replicas: manifestutils.GetDesiredReplicas(params.OtelCol),
PodManagementPolicy: "Parallel",
VolumeClaimTemplates: VolumeClaimTemplates(params.OtelCol),
PersistentVolumeClaimRetentionPolicy: params.OtelCol.Spec.PersistentVolumeClaimRetentionPolicy,
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8 changes: 7 additions & 1 deletion internal/manifests/manifestutils/replicas.go
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Expand Up @@ -7,8 +7,14 @@ import (
"github.com/open-telemetry/opentelemetry-operator/apis/v1beta1"
)

func GetInitialReplicas(otelCol v1beta1.OpenTelemetryCollector) *int32 {
func GetDesiredReplicas(otelCol v1beta1.OpenTelemetryCollector) *int32 {
// If autoscaling is configured, ensure we never set replicas below MinReplicas,
// but still respect Spec.Replicas which may be updated via the scale subresource (e.g., by HPA).
if otelCol.Spec.Autoscaler != nil && otelCol.Spec.Autoscaler.MinReplicas != nil {
if otelCol.Spec.Replicas != nil {
replicas := max(*otelCol.Spec.Autoscaler.MinReplicas, *otelCol.Spec.Replicas)
return &replicas
}
return otelCol.Spec.Autoscaler.MinReplicas
}
return otelCol.Spec.Replicas
Expand Down
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