Unable to get Instance from AWS lambda function Nodejs

Question

I have created a SNS topic a cloud watch event (to trigger alerts on any instance state change) & a lambda function to send notification to 3rd party apps when any such event is triggered.

Below is my Lambda code -:

var https = require('https');
var util = require('util');

exports.handler = function(event, context) {
    console.log(JSON.stringify(event, null, 2));
    console.log('From SNS:', event.Records[0].Sns.Message);

    var message = event.Records[0].Sns.Message;
    
    var postData = {
        "text": message
    };

    var options = {
        method: 'POST',
        hostname: 'hooks.slack.com',
        port: 443,
        path: process.env.CHAT_API_PATH
    };

    var req = https.request(options, function(res) {
      res.setEncoding('utf8');
      res.on('data', function (chunk) {
        context.done(null);
      });
    });
    
    req.on('error', function(e) {
      console.log('problem with request: ' + e.message);
    });    

    req.write(util.format("%j", postData));
    req.end();
};

The above code triggers a notification message on 3rd party app (Say on Slack channel) successfully and displays the message as below whenever any instance state is changed -:

{"version":"0","id":"c15cd3c9-d0aa-ca2e-71bb-c9b892c562c7","detail-type":"EC2 Instance State-change Notification","source":"aws.ec2","account":"288468818145","time":"2021-07-14T07:05:31Z","region":"us-east-1","resources":["arn:aws:ec2:us-east-1:288468818145:instance/i-0a3305ab8922ad61a"],"detail":{"instance-id":"i-0a3305ab8922ad61a","state":"stopping"}}

The only problem is, i want to display only "instance-id" and "state" of my instances in notification message and want my lambda to pass only these values how to do it ?

P.S. -: I don't want to touch SNS within cloudwatch target i.e. via "Input Transformer" to format my message instead want to handle it purely from Lambda.

By extracting only the interesting parts out of message / the event. Parse / interpret the json and only use the "detail" info. — luk2302

Ankur Vaish Ankur Vaish · Accepted Answer · 2021-07-18T08:41:21

After further study, got the way by adding json component within “Input transformer” in cloudwatch target.

This will simply extract the instance id and state from cloudwatch alert message and pass same to SNS which further gets into existing lambda function.

Unable to get Instance from AWS lambda function Nodejs

1 Answers