This is the lambda function that send slack notification.

slack_notification_lambda_function.js

const AWS = require('aws-sdk');
var url = require('url');
var https = require('https');
var util = require('util');
const p = require('phin');

const reqURL = `https://hooks.slack.com/services/TBCSBJ5/50117HG5HFV/hnfnDN78KJNH56RFVds`;

async function notifySlack() {

  const message = {
    'channel': '<Notification Slack channel>',
    'username': 'Build Server',
    'text': 'Jenkins: Open Jenkins Build server here',
    'icon_emoji': ':aws:',
    'attachments': [{
      'color': '#8697db',
      'fields': [
        {
          'title': 'EC2 server',
          'value': 'EC2 server Starting...',
          'short': true
        }
      ]
    }]
  };

  return p({
    url: reqURL,
    method: 'POST',
    data: message
  });
}

exports.handler = async (event, context, callback) => {
  context.callbackWaitsForEmptyEventLoop = false;
   const ec2 = new AWS.EC2({ region: event.instanceRegion });
    
    ec2.startInstances({ InstanceIds: [event.instanceId] }).promise()
        .then(() => callback(null, `Successfully started ${event.instanceId}`))
        .catch(err => callback(err));
  
  const req = await notifySlack();

};