lifecycle-poller Lambda with less characters

lib.js

let AWS = require('aws-sdk')
let ecs = new AWS.ECS()
let sqs = new AWS.SQS()
let asg = new AWS.AutoScaling()

let cluster = process.env.CLUSTER
let QueueUrl = process.env.QUEUE_URL
let drainingTimeout = process.env.DRAINING_TIMEOUT

async function getContainerInstanceArn(id) {
  let o = { cluster, filter: `ec2InstanceId == '${id}'` }
  console.log("getContainerInstanceArn(", o, ")")
  return (await ecs.listContainerInstances(o).promise()).containerInstanceArns[0]
}

async function countTasks(containerInstance) {
  let o = { cluster, containerInstance }
  console.log("countTasks(", o, ")")
  return (await ecs.listTasks(o).promise()).taskArns.length
}

function drainInstance(arn) {
  let o = { cluster, containerInstances: [arn], status: 'DRAINING' }
  console.log("drainInstance(", o, ")")
  return ecs.updateContainerInstancesState(o).promise()
}

function wait(r) {
  r = {
    Service: 'DrainInstance',
    Event: 'custom:DRAIN_WAIT',
    ContainerInstanceArn: r.ContainerInstanceArn,
    AutoScalingGroupName: r.AutoScalingGroupName,
    LifecycleHookName: r.LifecycleHookName,
    LifecycleActionToken: r.LifecycleActionToken,
    TerminateTime: r.TerminateTime,
  }
  console.log("wait(", r, ")")
  return sqs.sendMessage({
    QueueUrl,
    DelaySeconds: 60,
    MessageBody: JSON.stringify(r)
  }).promise()
}

function deleteMessage(ReceiptHandle) {
  let req = { QueueUrl, ReceiptHandle }
  console.log("deleteMessage(", req, ")")
  return sqs.deleteMessage(req).promise()
}

function terminateInstance(r) {
  r = {
    AutoScalingGroupName: r.AutoScalingGroupName,
    LifecycleHookName: r.LifecycleHookName,
    LifecycleActionToken: r.LifecycleActionToken,
    LifecycleActionResult: 'CONTINUE'
  }
  console.log("terminateInstance(", r, ")")
  return asg.completeLifecycleAction(r).promise()
}

function heartbeat(r) {
  r = {
    AutoScalingGroupName: r.AutoScalingGroupName,
    LifecycleHookName: r.LifecycleHookName,
    LifecycleActionToken: r.LifecycleActionToken,
  }
  console.log("heartbeat(", r, ")")
  return asg.recordLifecycleActionHeartbeat(r).promise()
}

exports.handler = async event => {
  console.log(`Invoke: ${JSON.stringify(event)}`)

  let rec = event.Records[0];
  let body = JSON.parse(rec.body)// batch size is 1

  if (body.Service === 'AWS Auto Scaling') {
    if (body.Event === 'autoscaling:TEST_NOTIFICATION') {
      console.log('Ignoring autoscaling:TEST_NOTIFICATION')
    } else if (body.LifecycleTransition === 'autoscaling:EC2_INSTANCE_TERMINATING') {
      body.ContainerInstanceArn = await getContainerInstanceArn(body.EC2InstanceId)
      body.TerminateTime = body.Time
      await Promise.all([drainInstance(body.ContainerInstanceArn), wait(body)])
    }
  } else if (body.Service === 'DrainInstance' && body.Event === 'custom:DRAIN_WAIT') {
    if (0 === await countTasks(body.ContainerInstanceArn)) {
      await terminateInstance(body)
    } else {
      let actionDuration = Math.abs(new Date(body.TerminateTime).getTime() - new Date().getTime()) / 1000
      if (actionDuration < drainingTimeout) {
        await Promise.all([heartbeat(body), wait(body)])
      } else {
        console.log('Timeout for instance termination reached.')
        await terminateInstance(body)
      }
    }
  } else {
    console.log('Ignoring invalid event ...')
  }
  await deleteMessage(rec.receiptHandle)
}