Application Auto Scaling

AWS Application Auto Scaling — scalable targets, step / target-tracking / predictive policies, scheduled actions, scaling activities, predictive forecasts, tags. JSON 1.1 protocol.

fakecloud implements AWS Application Auto Scaling's full JSON 1.1 control plane: 14 operations covering scalable targets, scaling policies, scheduled actions, scaling activities, predictive forecasts, and tags. 100% Smithy conformance.

Status: 100% control-plane coverage.

Supported today

  • Scalable targets — RegisterScalableTarget accepts ServiceNamespace, ResourceId, ScalableDimension, MinCapacity, MaxCapacity, RoleARN, SuspendedState. Re-registering an existing target only patches the supplied fields (PUT-merge). RoleARN defaults to the per-namespace service-linked role ARN (e.g. AWSServiceRoleForApplicationAutoScaling_ECSService). DescribeScalableTargets filters by ServiceNamespace + ResourceIds + ScalableDimension with MaxResults + NextToken pagination. DeregisterScalableTarget cascades: any ScalingPolicy or ScheduledAction for the same target is removed, so test state stays consistent. Supported namespaces include ecs, lambda, dynamodb, rds, elasticache, sagemaker, elasticmapreduce, appstream, cassandra, kafka, neptune, ec2, comprehend.
  • Scaling policies — PutScalingPolicy accepts PolicyName + PolicyType (StepScaling / TargetTrackingScaling / PredictiveScaling) and stores the corresponding configuration verbatim (round-tripped through DescribeScalingPolicies). Returns a deterministic PolicyARN and an empty Alarms list. Without a registered scalable target, returns ObjectNotFoundException. DescribeScalingPolicies filters by PolicyNames/ResourceId/ScalableDimension and paginates. DeleteScalingPolicy removes by name + target tuple.
  • Scheduled actions — PutScheduledAction accepts Schedule (at(...) / rate(...) / cron(...)), Timezone, StartTime, EndTime, ScalableTargetAction (MinCapacity/MaxCapacity). Existing actions PUT-merge supplied fields. DescribeScheduledActions paginates, filters by names + target. DeleteScheduledAction removes by name + target tuple. Targets must already be registered.
  • Scaling activities — DescribeScalingActivities returns the per-target activity log newest-first with IncludeNotScaledActivities filtering (default suppresses Failed).
  • Predictive scaling forecast — GetPredictiveScalingForecast requires the policy to be PolicyType = PredictiveScaling (otherwise ValidationException), then returns deterministic hourly Load + Capacity buckets between StartTime and EndTime capped at one week. Values are computed from the hour-of-day so tests can assert specific points.
  • Tags — TagResource upserts tag pairs keyed by ResourceARN, UntagResource removes by TagKeys, ListTagsForResource returns the current tag map. Unknown ARNs return ObjectNotFoundException.

Smoke test

fakecloud &

aws --endpoint-url http://localhost:4566 application-autoscaling register-scalable-target \
  --service-namespace ecs \
  --resource-id service/cluster/api \
  --scalable-dimension ecs:service:DesiredCount \
  --min-capacity 1 --max-capacity 10

aws --endpoint-url http://localhost:4566 application-autoscaling put-scaling-policy \
  --service-namespace ecs \
  --resource-id service/cluster/api \
  --scalable-dimension ecs:service:DesiredCount \
  --policy-name scale-out \
  --policy-type TargetTrackingScaling \
  --target-tracking-scaling-policy-configuration '{
    "TargetValue": 70.0,
    "PredefinedMetricSpecification": {"PredefinedMetricType": "ECSServiceAverageCPUUtilization"}
  }'

aws --endpoint-url http://localhost:4566 application-autoscaling describe-scaling-policies \
  --service-namespace ecs

Caveats

fakecloud does not actually scale anything. PutScalingPolicy and PutScheduledAction store configurations verbatim and return them on Describe*, but no metric is collected, no alarm is created, and ECS task counts / Lambda concurrency / DynamoDB capacity are never adjusted. Predictive forecasts are deterministic synthetic curves, not actual ML predictions — useful for asserting your code reads the response shape correctly, not for any business logic. Scaling activities are an in-memory log seeded by the service itself; fakecloud doesn't emit any. CloudWatch alarms reported under ScalingPolicy.Alarms are always empty.