AWS node.js deregister all unhealthy elastic load balancer targets

deregister_targets.js

const AWS = require('aws-sdk')

const elb = new AWS.ELBv2({apiVersion: '2015-12-01', region: 'us-east-1'})

async function getTGs(loadBalancerArn) {
  return new Promise((resolve, reject) => {
     elb.describeTargetGroups({}, (err, data) => {
        if (err) return reject(err)
        resolve(data.TargetGroups.map(x => x.TargetGroupArn))
      })
  })
}

async function getHealth(tg) {
  return new Promise((resolve, reject) => {
     elb.describeTargetHealth({
       TargetGroupArn: tg
    }, (err, data) => {
      if (err) return reject(err)
        resolve(data.TargetHealthDescriptions.map(x => {
          return {
            target: x.Target,
            state: x.TargetHealth.State,
          }
        }))
    })
  })
}

async function deregisterTargets(tgGroupArn, tgs) {
  return new Promise((resolve, reject) => {
    if (!tgs.length) {
      return resolve({targetGroupArn: tgGroupArn, message: 'nothing to deregister'})
    }

    elb.deregisterTargets({
      TargetGroupArn: tgGroupArn,
      Targets: tgs
    }, (err, data) => {
        if (err) return reject(err)
        resolve(data)
      })
  })
}

exports.handler = async (event, context, callback) => {
  const tgs = await getTGs()
  const data = await Promise.all(tgs.map(async tg => {
    const healths = await getHealth(tg)
    const unhealthy = healths.reduce((acc, x) => {
      if (x.state === 'unhealthy') {
        acc.push(x.target)
      }
      return acc
    }, [])

    return await deregisterTargets(tg, unhealthy)
  }))

  if (typeof callback == 'function') {
    callback(null, data)
  }

  console.log(data)
  return data
}