AWS Lambda function for forwarding SNS notifications to Slack

index.js

console.log('Loading function');

const https = require('https');
const url = require('url');
// to get the slack hook url, go into slack admin and create a new "Incoming Webhook" integration
const slack_url = 'https://hooks.slack.com/services/...';
const slack_req_opts = url.parse(slack_url);
slack_req_opts.method = 'POST';
slack_req_opts.headers = {'Content-Type': 'application/json'};

const pp = function(o) {
  return JSON.stringify(o, null, 2);
}

exports.handler = function(event, context) {
  (event.Records || []).forEach(function (rec) {
    if (rec.Sns) {
      var emoji = ":mailbox_with_mail:"; // default for icon_emoji
      var username = rec.Sns.TopicArn;   // use TopicArn as username
      var parsed = {};
      var text = "";

      var req = https.request(slack_req_opts, function (res) {
        if (res.statusCode === 200) {
          context.succeed('posted to slack');
        } else {
          context.fail('status code: ' + res.statusCode);
        }
      });

      req.on('error', function(e) {
        console.log('problem with request: ' + e.message);
        context.fail(e.message);
      });

      try {
          parsed = JSON.parse(rec.Sns.Message);

          // since we just want to see the JSON;
          // surrond json in code snippet brackets
          text = '```' + pp(parsed) + '```';

          // Parse the CloudWatch alarm message, set emoji based on that state
          // TODO: only post the StateValue and AlarmName to keep it clean.
          if (parsed.NewStateValue) {
            switch (parsed.NewStateValue){
              case "ALARM":
                emoji = ":alarm_clock:";
                break;
              case "OK":
                emoji = ":white_check_mark:";
                break;
              case "INSUFFICIENT_DATA":
                emoji = ":information_source:";
                break;
            }
            // use if you have frequent alarms...
            // text = emoji+"\n"+text;
            // or change the username to force icon_emoji to change
            // username = username + " " + parsed.NewStateValue;
          }
      }
      catch(e) {
        parsed = {};
        // if sns message is a string, just show it
        text = rec.Sns.Message;
      }

      // send the request, with the payload as the body
      req.write(JSON.stringify({
        text: text,
        username: username,
        icon_emoji: emoji
      }));

      req.end();
    }
  });
};

several improvements, more robust message handling

• used emoji parsing via JeffRausch/function.js
• uses icon_emoji to show the alarm state
• defaults to trying to parse the Ss.Message but fall backs to
  sending the message as a string (so it doesn’t show up with double
  quotes a la (JSON.stringify(“some string”));

renamed function.js to index.js to match default handler for lambda of index.handler