View autoscaler logs

When you enable autoscaling, the autoscaler makes scaling decisions based on the options that you specify. Each scaling decision is logged by Cloud Logging . Read these logs in the Logs Explorer to better understand the autoscaler's scaling decisions.

Using the Logs Explorer, you can see events related to:

• Autoscaler recommendation for resizing a managed instance group (MIG). If the autoscaler calculates a new recommended size for a MIG, the change in the recommended size is described in the autoscaler logs. See Resize log entry .
• Changes in autoscaler status. For example, if the autoscaler was working as expected but then encountered an issue, the change in status would be described in the autoscaler logs. See Status change log entry .

Before you begin

• Read the Autoscaling documentation.
• Have an active autoscaler for which you want to view logs.
• Review how to use the Logs Explorer .
• If you haven't already, set up authentication . Authentication verifies your identity for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:

  Select the tab for how you plan to use the samples on this page:

  Console

  When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.

  gcloud

  1. Install the Google Cloud CLI. After installation, initialize the Google Cloud CLI by running the following command:

     gcloud  
     init

     If you're using an external identity provider (IdP), you must first sign in to the gcloud CLI with your federated identity .

  2. Set a default region and zone .

  REST

  To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.

  Install the Google Cloud CLI. After installation, initialize the Google Cloud CLI by running the following command:

  gcloud  
  init

  If you're using an external identity provider (IdP), you must first sign in to the gcloud CLI with your federated identity .

  For more information, see Authenticate for using REST in the Google Cloud authentication documentation.

View autoscaler logs

To view autoscaler logs, use the Google Cloud console, the gcloud CLI, or REST.

gcloud logging read "resource.type=autoscaler" --limit 10 \
    --format json

gcloud logging read "resource.type=autoscaler AND \ resource.labels.instance_group_manager_name=example-igm 
" \
    --limit 10 --format json

gcloud logging read "resource.type=autoscaler AND \
    resource.labels.instance_group_manager_name=example-igm AND \ protoPayload.methodName=compute.autoscalers.resize" 
\
    --limit 10 --format json

gcloud logging read "resource.type=autoscaler AND \
    resource.labels.instance_group_manager_name=example-igm AND \ protoPayload.methodName=compute.autoscalers.changeStatus" 
\
    --limit 10 --format json

POST https://logging.googleapis.com/v2/entries:list

{
  "filter": "resource.type=autoscaler AND
    resource.labels.instance_group_manager_name=example-igm AND
    protoPayload.methodName=compute.autoscalers.resize",
  "pageSize": 10,
  "resourceNames": [
    "projects/example-project"
  ]
}

POST https://logging.googleapis.com/v2/entries:list

{
  "filter": "resource.type=autoscaler AND
    resource.labels.instance_group_manager_name=example-igm AND
    protoPayload.methodName=compute.autoscalers.changeStatus",
  "pageSize": 10,
  "resourceNames": [
    "projects/example-project"
  ]
}

Resize log entry

When the autoscaler calculates a recommended size for your MIG, Compute Engine creates a log entry capturing the new and old recommended sizes. For zonal MIGs, the log entry also captures the reason for the change in recommended size.

The following is an example of a log entry for a zonal MIG. In this example, based on predictive autoscaling the autoscaler calculated 3 VMs to achieve the CPU utilization target of 35% . But, the maximum number of instances configured in the autoscaling policy is only 2 . So, the autoscaler limits the recommended size to 2 .

{
    insertId: "1l68z7sg4jw7kzo"
    logName: "projects/example-project/logs/cloudaudit.googleapis.com%2Fsystem_event"
    protoPayload: {
      @type: "type.googleapis.com/google.cloud.audit.AuditLog"
      metadata: {
        @type: "type.googleapis.com/autoscaler.AutoscalerSizeChangeExplanation"
        autoscalingMode: "ON" autoscalingReason 
: {
          scalingLimit: {
            limitPolicy: {
              maxNumReplicas: 2
            }
            limitSize: 2
            name: "MAX_INSTANCES"
          }
          scalingSignal: {
            calculatedSize: 3
            calculationDetails: {
              servingSize: 1
              signalTarget: 0.35
              signalValue: 1.03533
            }
            name: "PREDICTED_CPU_UTILIZATION"
            signalPolicy: {
              coolDownPeriodSec: 15
              cpuUtilization: {
                predictiveMethod: "OPTIMIZE_AVAILABILITY"
                utilizationTarget: 0.35
              }
            }
          }
          summary: "The autoscaler's recommended size changed from 1 to 2
          because the autoscaler predicted that in 15 seconds the average CPU
          utilization across 1 serving instance will be 103.533%, which is above
          the utilization target of 35%. The calculated size was 3 to achieve
          the target CPU utilization but the size was limited by the maximum
          number of instances set in the autoscaling policy."
        } newSize: 2
        oldSize: 1 
} methodName: "compute.autoscalers.resize" 
resourceName: "projects/example-project/zones/us-east1-d/autoscalers/example-autoscaler"
      serviceName: "compute.googleapis.com"
    }
    receiveTimestamp: "2022-06-13T22:34:43.045973046Z"
    resource: {
      labels: {
        autoscaler_id: "1234567890123456789"
        autoscaler_name: "example-autoscaler"
        instance_group_manager_id: "1357908642148074125"
        instance_group_manager_name: "example-igm"
        location: "us-east1-d"
        project_id: "example-project"
      }
      type: "autoscaler"
    }
    severity: "INFO"
    timestamp: "2022-06-13T22:34:42.810216614Z"
    }

The following table describes the fields from the log entry:

For information about the other fields in the log entry, see Format of audit log entries .

Status change log entry

When the status of the autoscaler changes, Compute Engine creates a log entry capturing the old and new status messages. You can use these status messages to find out why your autoscaler is not behaving as you expect or to debug past issues you noticed. For some of the common status messages, see Commonly returned status messages .

The following fields in the protoPayload describe the old and new statuses:

• metadata.newStatus.details : The new status of the autoscaler.
• metadata.oldStatus.details : The previous status of the autoscaler.

The following is an example of a log entry that describes a status change. In this example, you might notice the new status message indicating problems with your load balancing configuration.

{
      insertId: "ivho6kg4icqfio"
      logName: "projects/example-project/logs/cloudaudit.googleapis.com%2Fsystem_event"
      protoPayload: {
        metadata: {
          @type: "type.googleapis.com/autoscaler.AutoscalerStatusChange" newStatus 
: {
            details: "The autoscaler is configured to scale based on a load
            balancing signal but the instance group has not received any
            utilization data from the load balancer or the utilization is
            constantly 0. Check that the load balancing configuration is
            working"
          } oldStatus 
: {
            details: "OK"
          }, methodName: "compute.autoscalers.changeStatus" 
resourceName: "projects/example-project/zones/us-east1-b/autoscalers/example-autoscaler"
          serviceName: "compute.googleapis.com"
        }
        receiveTimestamp: "2022-06-08T03:54:12.332329320Z"
        resource: {
          labels: {
            autoscaler_id: "1234567890123456789"
            autoscaler_name: "example-autoscaler"
            instance_group_manager_id: "1357908642148074125"
            instance_group_manager_name: "example-igm"
            location: "us-east1-b"
            project_id: "example-project"
          }
          type: "autoscaler"
        }
        severity: "INFO"
        timestamp: "2022-06-08T03:54:10.675416812Z"
      }
    }

For information about the other fields in the log entry, see Format of audit log entries .

What's next

• Update your autoscaler using information that you received from the logs.
• Learn how autoscaler makes decisions .
• Review autoscaling options .