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target-tracking-scaling-policy.ts
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target-tracking-scaling-policy.ts
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import * as cloudwatch from '@aws-cdk/aws-cloudwatch';
import * as cdk from '@aws-cdk/core';
import { IAutoScalingGroup } from './auto-scaling-group';
import { CfnScalingPolicy } from './autoscaling.generated';
/**
* Base interface for target tracking props
*
* Contains the attributes that are common to target tracking policies,
* except the ones relating to the metric and to the scalable target.
*
* This interface is reused by more specific target tracking props objects.
*/
export interface BaseTargetTrackingProps {
/**
* Indicates whether scale in by the target tracking policy is disabled.
*
* If the value is true, scale in is disabled and the target tracking policy
* won't remove capacity from the autoscaling group. Otherwise, scale in is
* enabled and the target tracking policy can remove capacity from the
* group.
*
* @default false
*/
readonly disableScaleIn?: boolean;
/**
* Period after a scaling completes before another scaling activity can start.
*
* @default - The default cooldown configured on the AutoScalingGroup.
*/
readonly cooldown?: cdk.Duration;
/**
* Estimated time until a newly launched instance can send metrics to CloudWatch.
*
* @default - Same as the cooldown.
*/
readonly estimatedInstanceWarmup?: cdk.Duration;
}
/**
* Properties for a Target Tracking policy that include the metric but exclude the target
*/
export interface BasicTargetTrackingScalingPolicyProps extends BaseTargetTrackingProps {
/**
* The target value for the metric.
*/
readonly targetValue: number;
/**
* A predefined metric for application autoscaling
*
* The metric must track utilization. Scaling out will happen if the metric is higher than
* the target value, scaling in will happen in the metric is lower than the target value.
*
* Exactly one of customMetric or predefinedMetric must be specified.
*
* @default - No predefined metric.
*/
readonly predefinedMetric?: PredefinedMetric;
/**
* A custom metric for application autoscaling
*
* The metric must track utilization. Scaling out will happen if the metric is higher than
* the target value, scaling in will happen in the metric is lower than the target value.
*
* Exactly one of customMetric or predefinedMetric must be specified.
*
* @default - No custom metric.
*/
readonly customMetric?: cloudwatch.IMetric;
/**
* The resource label associated with the predefined metric
*
* Should be supplied if the predefined metric is ALBRequestCountPerTarget, and the
* format should be:
*
* app/<load-balancer-name>/<load-balancer-id>/targetgroup/<target-group-name>/<target-group-id>
*
* @default - No resource label.
*/
readonly resourceLabel?: string;
}
/**
* Properties for a concrete TargetTrackingPolicy
*
* Adds the scalingTarget.
*/
export interface TargetTrackingScalingPolicyProps extends BasicTargetTrackingScalingPolicyProps {
/*
* The auto scaling group
*/
readonly autoScalingGroup: IAutoScalingGroup;
}
export class TargetTrackingScalingPolicy extends cdk.Construct {
/**
* ARN of the scaling policy
*/
public readonly scalingPolicyArn: string;
/**
* The resource object
*/
private resource: CfnScalingPolicy;
constructor(scope: cdk.Construct, id: string, props: TargetTrackingScalingPolicyProps) {
if ((props.customMetric === undefined) === (props.predefinedMetric === undefined)) {
throw new Error('Exactly one of \'customMetric\' or \'predefinedMetric\' must be specified.');
}
if (props.predefinedMetric === PredefinedMetric.ALB_REQUEST_COUNT_PER_TARGET && !props.resourceLabel) {
throw new Error('When tracking the ALBRequestCountPerTarget metric, the ALB identifier must be supplied in resourceLabel');
}
if (props.customMetric && !props.customMetric.toMetricConfig().metricStat) {
throw new Error('Only direct metrics are supported for Target Tracking. Use Step Scaling or supply a Metric object.');
}
super(scope, id);
this.resource = new CfnScalingPolicy(this, 'Resource', {
policyType: 'TargetTrackingScaling',
autoScalingGroupName: props.autoScalingGroup.autoScalingGroupName,
cooldown: props.cooldown && props.cooldown.toSeconds().toString(),
estimatedInstanceWarmup: props.estimatedInstanceWarmup && props.estimatedInstanceWarmup.toSeconds(),
targetTrackingConfiguration: {
customizedMetricSpecification: renderCustomMetric(props.customMetric),
disableScaleIn: props.disableScaleIn,
predefinedMetricSpecification: props.predefinedMetric !== undefined ? {
predefinedMetricType: props.predefinedMetric,
resourceLabel: props.resourceLabel,
} : undefined,
targetValue: props.targetValue,
},
});
this.scalingPolicyArn = this.resource.ref;
}
}
function renderCustomMetric(metric?: cloudwatch.IMetric): CfnScalingPolicy.CustomizedMetricSpecificationProperty | undefined {
if (!metric) { return undefined; }
const c = metric.toMetricConfig().metricStat!;
return {
dimensions: c.dimensions,
metricName: c.metricName,
namespace: c.namespace,
statistic: c.statistic,
unit: c.unitFilter,
};
}
/**
* One of the predefined autoscaling metrics
*/
export enum PredefinedMetric {
/**
* Average CPU utilization of the Auto Scaling group
*/
ASG_AVERAGE_CPU_UTILIZATION = 'ASGAverageCPUUtilization',
/**
* Average number of bytes received on all network interfaces by the Auto Scaling group
*/
ASG_AVERAGE_NETWORK_IN = 'ASGAverageNetworkIn',
/**
* Average number of bytes sent out on all network interfaces by the Auto Scaling group
*/
ASG_AVERAGE_NETWORK_OUT = 'ASGAverageNetworkOut',
/**
* Number of requests completed per target in an Application Load Balancer target group
*
* Specify the ALB to look at in the `resourceLabel` field.
*/
ALB_REQUEST_COUNT_PER_TARGET = 'ALBRequestCountPerTarget',
}