slack notification for cloudwatch alerts

handler.py

##### To use: Setup a sns topic like cloudwatch-sns-slack.
### Enter webhook url in SLACK_URL; and change SLACK_CHANNEL;

import boto3
import json
import logging
import os
from base64 import b64decode
from urllib.request import Request, urlopen
from urllib.error import URLError, HTTPError

SLACK_CHANNEL = "<enter your slack channel here>"

SLACK_URL = "<enter your slack webhook url here>"

logger = logging.getLogger()
logger.setLevel(logging.INFO)

def lambda_handler(event, context):
    logger.info("Event: " + str(event))
    message = json.loads(event['Records'][0]['Sns']['Message'])
    logger.info("Message: " + str(message))

    alarm_name = message['AlarmName']
    new_state = message['NewStateValue']
    reason = message['NewStateReason']
    metric = message['Trigger']['MetricName']
    dimensions = message['Trigger']['Dimensions'][0]
    
    if new_state == 'ALARM':
      slack_message = {
        'channel': SLACK_CHANNEL,
        'text': "OMG!!! :fire: *Alert Triggered*: {} \n *State*: `{}` \n *Reason*: {} \n *Metrics*: {} \n *Resource*: {}" .format(alarm_name, new_state, reason, metric,dimensions)
      }
    else:
      slack_message = {
        'channel': SLACK_CHANNEL,
        'text': "Hey there!! :celebrate: {} \n *State*: `{}` \n *Reason*: {} \n *Metrics*: {} \n *Resource*: {}" .format(alarm_name, new_state, reason, metric,dimensions)
      }
  
    req = Request(SLACK_URL, json.dumps(slack_message).encode('utf-8'))
    try:
        response = urlopen(req)
        response.read()
        logger.info("delivered to", slack_message['channel'])
    except HTTPError as e:
        logger.error("Request failed: %d %s", e.code, e.reason)
    except URLError as e:
        logger.error("Conn failed: %s", e.reason)