Sagemaker async inference doesn't scale down to zero

cHello everyone,

I try according to the following instructions:

https://docs.aws.amazon.com/sagemaker/latest/dg/async-inference-autoscale.html

to scale an asynchronous endpoint to 0 if no requests come in or to scale it up if there are any in the queue. I have created the policy and the cloud watch alarm, but the instance always remains at 1:

I always have to specify at least 1 instance when creating the asynchronous production variant. Perhaps the problem is related to this.

I would be very happy to receive information on this, as scaling to 0 is a very important Feature for us. I've created this script:

import boto3
import json

#https://docs.aws.amazon.com/sagemaker/latest/dg/async-inference-autoscale.html

client = boto3.client('application-autoscaling') 
endpoint = "websites-document-clf-endpoint-async"
resource_id=f'endpoint/{endpoint}/variant/async-variant'

resource_id = (resource_id)
response = client.register_scalable_target(
	ServiceNamespace="sagemaker",
	ResourceId=resource_id,
	ScalableDimension="sagemaker:variant:DesiredInstanceCount",
	MinCapacity=0,
	MaxCapacity=5,
)

print(json.dumps(response, indent=4))

response = client.put_scaling_policy(
	PolicyName="HasBacklogWithoutCapacity-ScalingPolicy",
	ServiceNamespace="sagemaker",  # The namespace of the service that provides the resource.
	ResourceId=resource_id,  # Endpoint name
	ScalableDimension="sagemaker:variant:DesiredInstanceCount",  # SageMaker supports only Instance Count
	PolicyType="StepScaling",  # 'StepScaling' or 'TargetTrackingScaling'
	StepScalingPolicyConfiguration={
		"AdjustmentType": "ChangeInCapacity", # Specifies whether the ScalingAdjustment value in the StepAdjustment property is an absolute number or a percentage of the current capacity.
		"MetricAggregationType": "Average", # The aggregation type for the CloudWatch metrics.
		"Cooldown": 300, # The amount of time, in seconds, to wait for a previous scaling activity to take effect.
		"StepAdjustments": # A set of adjustments that enable you to scale based on the size of the alarm breach.
		[
			{
			  "MetricIntervalLowerBound": 0,
			  "ScalingAdjustment": 1
			}
		  ]
	},
)

print(json.dumps(response, indent=4))


cw_client = boto3.client('cloudwatch')

cw_response = cw_client.put_metric_alarm(
	AlarmName='HasBacklogWithoutCapacity-ScalingPolicy-Alarm',
	MetricName='HasBacklogWithoutCapacity',
	Namespace='AWS/SageMaker',
	Statistic='Average',
	EvaluationPeriods= 2,
	DatapointsToAlarm= 2,
	Threshold= 1,
	ComparisonOperator='GreaterThanOrEqualToThreshold',
	TreatMissingData='missing',
	Dimensions=[
		{ 'Name':'EndpointName', 'Value':endpoint },
	],
	Period= 60,
	AlarmActions=[response['PolicyARN']]
)

print(json.dumps(cw_response, indent=4))

Thx for any kind of help!