handler.js

'use strict';
const AWS = require('aws-sdk');
const TAG = process.env.TAG
const SNS_TOPIC_ARN = process.env.SNS_TOPIC_ARN
const ec2 = new AWS.EC2()


// Used to send a notification to SNS 
const sendNotification = async (subject, instanceIds) => {
  console.log(await new AWS.SNS().publish({
    TopicArn : SNS_TOPIC_ARN,
    Subject : subject,
    Message : `Instance Ids: ${instanceIds}`
  }).promise())
}


// Asks EC2 for a list of instances in the given state and returns their
// instance IDs.
const getSleepyInstances = async (state) => {
  const filter  = { Filters: [{Name: "tag:" + TAG, Values: ["True"]}] };
  const results = await new AWS.EC2().describeInstances(filter).promise();
  const ids  = [];

  (results.Reservations || []).forEach(r => r.Instances.
      filter(i => i.State.Name == state).
      forEach(i => ids.push(i.InstanceId)))

  return ids;
}


// Performs a start or stop instance action on any tagged instances
// in the given state, then publishes a notification to SNS.
const sleepcycle = async (state, message, action) => {
  try {
    const instanceIds = await getSleepyInstances(state);
    if (instanceIds.length > 0) {
      await action(instanceIds)
      if (SNS_TOPIC_ARN) await sendNotification(message, instanceIds)
    }
    return {
      statusCode: 200,
      message,
      body: JSON.stringify({ ids: instanceIds }, null, 2),
    };
  } catch (e) {
    console.log(e)
    throw e
  }
}

// Lambda endpoint for starting instances
module.exports.goodmorning = async () => 
  await sleepcycle('stopped', 'Instances waking up',
    (async ids => await ec2.startInstances({ InstanceIds: ids }).promise()))


// Lambda endpoint for stopping instances
module.exports.goodnight = async () => 
  await sleepcycle('running', 'Instances going to sleep',
    (async ids => await ec2.stopInstances({ InstanceIds: ids }).promise()))