Auto Scaling: Target Tracking with Metric Math

put-scaling-policy.sh

aws autoscaling put-scaling-policy \
--auto-scaling-group-name ASG_NAME \
--policy-name target-tracking \
--policy-type TargetTrackingScaling \
--target-tracking-configuration file://target-tracking-configuration.json \
--estimated-instance-warmup 300

target-tracking-configuration.json

{
  "CustomizedMetricSpecification": {
    "Metrics": [
      {
        "Id": "messages",
        "MetricStat": {
          "Metric": {
            "Namespace": "AWS/SQS",
            "MetricName": "ApproximateNumberOfMessagesVisible",
            "Dimensions": [
              {
                "Name": "QueueName",
                "Value": "QUEUE_NAME"
              }
            ]
          },
          "Stat": "Maximum",
          "Unit": "Count"
        },
        "Label": "Enqueued Messages",
        "ReturnData": false
      },
      {
        "Id": "instances",
        "MetricStat": {
          "Metric": {
            "Namespace": "AWS/AutoScaling",
            "MetricName": "GroupTotalInstances",
            "Dimensions": [
              {
                "Name": "AutoScalingGroupName",
                "Value": "ASG_NAME"
              }
            ]
          },
          "Stat": "Maximum",
          "Unit": "Count"
        },
        "Label": "Instances",
        "ReturnData": false
      },
      {
        "Id": "e1",
        "Expression": "FILL(instances, 1)",
        "Label": "E1",
        "ReturnData": false
      },
      {
        "Id": "e2",
        "Expression": "messages/IF(e1>0, e1, 1)",
        "Label": "E2",
        "ReturnData": true
      }
    ]
  },
  "TargetValue": 0.0001,
  "DisableScaleIn": false
}