warm-pool.ts

import { Lazy, Names, Resource } from '@aws-cdk/core';
import { Construct } from 'constructs';
import { IAutoScalingGroup } from './auto-scaling-group';
import { CfnWarmPool } from './autoscaling.generated';

/**
 * Options for a warm pool
 */
export interface WarmPoolOptions {
  /**
   * Indicates whether instances in the Auto Scaling group can be returned to the warm pool on scale in.
   *
   * If the value is not specified, instances in the Auto Scaling group will be terminated
   * when the group scales in.
   *
   * @default - false
   */
  readonly reuseOnScaleIn?: boolean;

  /**
   * The maximum number of instances that are allowed to be in the warm pool
   * or in any state except Terminated for the Auto Scaling group.
   *
   * If the value is not specified, Amazon EC2 Auto Scaling launches and maintains
   * the difference between the group's maximum capacity and its desired capacity.
   *
   * @default - max size of the Auto Scaling group
   */
  readonly maxGroupPreparedCapacity?: number;
  /**
   * The minimum number of instances to maintain in the warm pool.
   *
   * @default - 0
   */
  readonly minSize?: number;
  /**
   * The instance state to transition to after the lifecycle actions are complete.
   *
   * @default - STOPPED
   */
  readonly poolState?: PoolState;
}

/**
 * Properties for a warm pool
 */
export interface WarmPoolProps extends WarmPoolOptions {
  /**
   * The Auto Scaling group to add the warm pool to.
   */
  readonly autoScalingGroup: IAutoScalingGroup;
}

/**
 * Define a warm pool
 */
export class WarmPool extends Resource {
  constructor(scope: Construct, id: string, props: WarmPoolProps) {
    super(scope, id, {
      physicalName: Lazy.string({ produce: () => Names.uniqueId(this) }),
    });

    if (props.maxGroupPreparedCapacity && props.maxGroupPreparedCapacity < -1) {
      throw new Error('\'maxGroupPreparedCapacity\' parameter should be greater than or equal to -1');
    }

    if (props.minSize && props.minSize < 0) {
      throw new Error('\'minSize\' parameter should be greater than or equal to 0');
    }

    new CfnWarmPool(this, 'Resource', {
      autoScalingGroupName: props.autoScalingGroup.autoScalingGroupName,
      instanceReusePolicy: props.reuseOnScaleIn !== undefined ? {
        reuseOnScaleIn: props.reuseOnScaleIn,
      } : undefined,
      maxGroupPreparedCapacity: props.maxGroupPreparedCapacity,
      minSize: props.minSize && props.minSize,
      poolState: props.poolState && props.poolState,
    });
  }
}

/**
 * The instance state in the warm pool
 */
export enum PoolState {
  /**
   * Hibernated
   *
   * To use this state, prerequisites must be in place.
   * @see https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/hibernating-prerequisites.html
   */
  HIBERNATED = 'Hibernated',

  /**
   * Running
   */
  RUNNING = 'Running',

  /**
   * Stopped
   */
  STOPPED = 'Stopped',
}