REST Resource: regionAutoscalers

Resource: Autoscaler

Represents an Autoscaler resource.

Google Compute Engine has two Autoscaler resources:

Use autoscalers to automatically add or delete instances from a managed instance group according to your defined autoscaling policy. For more information, read Autoscaling Groups of Instances.

For zonal managed instance groups resource, use the autoscaler resource.

For regional managed instance groups, use the regionAutoscalers resource.

JSON representation
  "id": string,
  "creationTimestamp": string,
  "name": string,
  "description": string,
  "target": string,
  "autoscalingPolicy": {
    "minNumReplicas": integer,
    "maxNumReplicas": integer,
    "scaleInControl": {
      "maxScaledInReplicas": {
        "fixed": integer,
        "percent": integer,
        "calculated": integer
      "timeWindowSec": integer
    "coolDownPeriodSec": integer,
    "cpuUtilization": {
      "utilizationTarget": number
    "customMetricUtilizations": [
        "metric": string,
        "utilizationTargetType": enum,
        "utilizationTarget": number
    "loadBalancingUtilization": {
      "utilizationTarget": number
    "mode": enum
  "zone": string,
  "region": string,
  "selfLink": string,
  "status": enum,
  "statusDetails": [
      "message": string,
      "type": enum
  "recommendedSize": integer,
  "kind": string

string (fixed64 format)

[Output Only] The unique identifier for the resource. This identifier is defined by the server.



[Output Only] Creation timestamp in RFC3339 text format.



Name of the resource. Provided by the client when the resource is created. The name must be 1-63 characters long, and comply with RFC1035. Specifically, the name must be 1-63 characters long and match the regular expression [a-z]([-a-z0-9]*[a-z0-9])? which means the first character must be a lowercase letter, and all following characters must be a dash, lowercase letter, or digit, except the last character, which cannot be a dash.



An optional description of this resource. Provide this property when you create the resource.



URL of the managed instance group that this autoscaler will scale.



The configuration parameters for the autoscaling algorithm. You can define one or more of the policies for an autoscaler: cpuUtilization, customMetricUtilizations, and loadBalancingUtilization.

If none of these are specified, the default will be to autoscale based on cpuUtilization to 0.6 or 60%.



The minimum number of replicas that the autoscaler can scale down to. This cannot be less than 0. If not provided, autoscaler will choose a default value depending on maximum number of instances allowed.



The maximum number of instances that the autoscaler can scale up to. This is required when creating or updating an autoscaler. The maximum number of replicas should not be lower than minimal number of replicas.





Maximum allowed number (or %) of VMs that can be deducted from the peak recommendation during the window autoscaler looks at when computing recommendations. Possibly all these VMs can be deleted at once so user service needs to be prepared to lose that many VMs in one step.



Specifies a fixed number of VM instances. This must be a positive integer.



Specifies a percentage of instances between 0 to 100%, inclusive. For example, specify 80 for 80%.



[Output Only] Absolute value of VM instances calculated based on the specific mode.

  • If the value is fixed, then the calculated value is equal to the fixed value.
  • If the value is a percent, then the calculated value is percent/100 * targetSize. For example, the calculated value of a 80% of a managed instance group with 150 instances would be (80/100 * 150) = 120 VM instances. If there is a remainder, the number is rounded up.


How long back autoscaling should look when computing recommendations to include directives regarding slower scale in, as described above.



The number of seconds that the autoscaler should wait before it starts collecting information from a new instance. This prevents the autoscaler from collecting information when the instance is initializing, during which the collected usage would not be reliable. The default time autoscaler waits is 60 seconds.

Virtual machine initialization times might vary because of numerous factors. We recommend that you test how long an instance may take to initialize. To do this, create an instance and time the startup process.



Defines the CPU utilization policy that allows the autoscaler to scale based on the average CPU utilization of a managed instance group.



The target CPU utilization that the autoscaler should maintain. Must be a float value in the range (0, 1]. If not specified, the default is 0.6.

If the CPU level is below the target utilization, the autoscaler scales down the number of instances until it reaches the minimum number of instances you specified or until the average CPU of your instances reaches the target utilization.

If the average CPU is above the target utilization, the autoscaler scales up until it reaches the maximum number of instances you specified or until the average utilization reaches the target utilization.



Configuration parameters of autoscaling based on a custom metric.



The identifier (type) of the Stackdriver Monitoring metric. The metric cannot have negative values.

The metric must have a value type of INT64 or DOUBLE.



The target value of the metric that autoscaler should maintain. This must be a positive value. A utilization metric scales number of virtual machines handling requests to increase or decrease proportionally to the metric.

For example, a good metric to use as a utilizationTarget is The autoscaler will work to keep this value constant for each of the instances.



Defines how target utilization value is expressed for a Stackdriver Monitoring metric. Either GAUGE, DELTA_PER_SECOND, or DELTA_PER_MINUTE.



Configuration parameters of autoscaling based on load balancer.



Fraction of backend capacity utilization (set in HTTP(S) load balancing configuration) that autoscaler should maintain. Must be a positive float value. If not defined, the default is 0.8.



Defines operating mode for this policy.



[Output Only] URL of the zone where the instance group resides (for autoscalers living in zonal scope).



[Output Only] URL of the region where the instance group resides (for autoscalers living in regional scope).



[Output Only] The status of the autoscaler configuration. Current set of possible values:

  • PENDING: Autoscaler backend hasn't read new/updated configuration.
  • DELETING: Configuration is being deleted.
  • ACTIVE: Configuration is acknowledged to be effective. Some warnings might be present in the statusDetails field.
  • ERROR: Configuration has errors. Actionable for users. Details are present in the statusDetails field.
New values might be added in the future.



[Output Only] Human-readable details about the current state of the autoscaler. Read the documentation for Commonly returned status messages for examples of status messages you might encounter.



The status message.



The type of error, warning, or notice returned. Current set of possible values:

  • ALL_INSTANCES_UNHEALTHY (WARNING): All instances in the instance group are unhealthy (not in RUNNING state).
  • BACKEND_SERVICE_DOES_NOT_EXIST (ERROR): There is no backend service attached to the instance group.
  • CAPPED_AT_MAX_NUM_REPLICAS (WARNING): Autoscaler recommends a size greater than maxNumReplicas.
  • CUSTOM_METRIC_DATA_POINTS_TOO_SPARSE (WARNING): The custom metric samples are not exported often enough to be a credible base for autoscaling.
  • CUSTOM_METRIC_INVALID (ERROR): The custom metric that was specified does not exist or does not have the necessary labels.
  • MIN_EQUALS_MAX (WARNING): The minNumReplicas is equal to maxNumReplicas. This means the autoscaler cannot add or remove instances from the instance group.
  • MISSING_CUSTOM_METRIC_DATA_POINTS (WARNING): The autoscaler did not receive any data from the custom metric configured for autoscaling.
  • MISSING_LOAD_BALANCING_DATA_POINTS (WARNING): The autoscaler is configured to scale based on a load balancing signal but the instance group has not received any requests from the load balancer.
  • MODE_OFF (WARNING): Autoscaling is turned off. The number of instances in the group won't change automatically. The autoscaling configuration is preserved.
  • MODE_ONLY_UP (WARNING): Autoscaling is in the "Autoscale only up" mode. The autoscaler can add instances but not remove any.
  • MORE_THAN_ONE_BACKEND_SERVICE (ERROR): The instance group cannot be autoscaled because it has more than one backend service attached to it.
  • NOT_ENOUGH_QUOTA_AVAILABLE (ERROR): There is insufficient quota for the necessary resources, such as CPU or number of instances.
  • REGION_RESOURCE_STOCKOUT (ERROR): Shown only for regional autoscalers: there is a resource stockout in the chosen region.
  • SCALING_TARGET_DOES_NOT_EXIST (ERROR): The target to be scaled does not exist.
  • UNSUPPORTED_MAX_RATE_LOAD_BALANCING_CONFIGURATION (ERROR): Autoscaling does not work with an HTTP/S load balancer that has been configured for maxRate.
  • ZONE_RESOURCE_STOCKOUT (ERROR): For zonal autoscalers: there is a resource stockout in the chosen zone. For regional autoscalers: in at least one of the zones you're using there is a resource stockout.
New values might be added in the future. Some of the values might not be available in all API versions.



[Output Only] Target recommended MIG size (number of instances) computed by autoscaler. Autoscaler calculates recommended MIG size even when autoscaling policy mode is different from ON. This field is empty when autoscaler is not connected to the existing managed instance group or autoscaler did not generate its prediction.



[Output Only] Type of the resource. Always compute#autoscaler for autoscalers.



Deletes the specified autoscaler.


Returns the specified autoscaler.


Creates an autoscaler in the specified project using the data included in the request.


Retrieves a list of autoscalers contained within the specified region.


Updates an autoscaler in the specified project using the data included in the request.


Updates an autoscaler in the specified project using the data included in the request.