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desiredReplicas ignored in scaledObject with trigger cron
Report
desiredReplicas
is ignored completely when using trigger cron for CRD based deployment
ScaledObject:
apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
name: backend
namespace: test
spec:
scaleTargetRef:
apiVersion: deployment.xxx.com/v1alpha1
kind: ApplicationDeployment
name: backend
triggers:
- metadata:
desiredReplicas: '5'
end: 30 * * * *
start: 0 * * * *
timezone: Europe/Riga
type: cron
Expected Behavior
desiredReplicas
should be respected by scaledObject cron based feature
triggers:
- metadata:
desiredReplicas: '5'
Actual Behavior
ScaledObject ref always restored to replicas: 1
ignoring desiredReplicas
2024-05-15T11:00:11Z INFO scaleexecutor Successfully updated ScaleTarget {"scaledobject.Name": "backend", "scaledObject.Namespace": "ivp-test", "scaleTarget.Name": "backend", "Original Replicas Count": 0, "New Replicas Count": 1}
Steps to Reproduce the Problem
- Create CRD based deployment with replicas = 5
- Create ScaledObject for the ref in step1 with
triggers: -metadata: desiredReplicas: '5'
- Wait for scale down action
- Wait for scale up action
Logs from KEDA operator
2024-05-15T10:33:11Z INFO scaleexecutor Successfully set ScaleTarget replicas count to ScaledObject minReplicaCount {"scaledobject.Name": "backend", "scaledObject.Namespace": "ivp-test", "scaleTarget.Name": "backend", "Original Replicas Count": 5, "New Replicas Count": 0}
2024-05-15T11:00:11Z INFO scaleexecutor Successfully updated ScaleTarget {"scaledobject.Name": "backend", "scaledObject.Namespace": "ivp-test", "scaleTarget.Name": "backend", "Original Replicas Count": 0, "New Replicas Count": 1}
KEDA Version
2.14.0
Kubernetes Version
1.27
Platform
Microsoft Azure
Scaler Details
No response
Anything else?
No response
This is by design, I believe, but I still think we should kill it in favor of https://github.com/kedacore/keda/issues/3566 @kedacore/keda-maintainers
What exactly is by design here? desiredReplicas
is a part of ScaledObject/triggers
spec and it's not working as expected.
Hello @gerbil It's working as expected because the scaling to 5 is happening, as we can see here:
2024-05-15T10:33:11Z INFO scaleexecutor Successfully set ScaleTarget replicas count to ScaledObject minReplicaCount {"scaledobject.Name": "backend", "scaledObject.Namespace": "ivp-test", "scaleTarget.Name": "backend", "Original Replicas Count": 5, "New Replicas Count": 0}
KEDA is scaling from 0 to 1 because KEDA relies on the HPA to scaling from 1 to N, so the "usual" process is that KEDA scales from 0 to 1 when there is at least 1 active trigger, and then the HPA scales the workload from 1 to N. desiredReplicas
is the value that the trigger will return to the HPA Controller. In the same way as with other scalers, if your queue returns 50, KEDA won't scale from 0 to 50 directly.
This is explained here: https://keda.sh/docs/2.14/concepts/scaling-deployments/#activating-and-scaling-thresholds
Given this, if you want to scale from 0 to 5 directly, it's doable. You can use idleReplicaCount
option to allow scaling to 0 with min replicas 5, and then KEDA will scaling from 0 to 5 and from 5 to 0 without passing from 1 and the HPA:
apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
name: backend
namespace: test
spec:
minReplicaCount: 5
idleReplicaCount: 0
scaleTargetRef:
apiVersion: deployment.xxx.com/v1alpha1
kind: ApplicationDeployment
name: backend
triggers:
- metadata:
desiredReplicas: '5'
end: 30 * * * *
start: 0 * * * *
timezone: Europe/Riga
type: cron