clowdwatch_to_slack.py

import boto3
import json
import logging
import os

from base64 import b64decode
from urllib.request import Request, urlopen
from urllib.error import URLError, HTTPError


# The base-64 encoded, encrypted key (CiphertextBlob) stored in the kmsEncryptedHookUrl environment variable
ENCRYPTED_HOOK_URL = os.environ['kmsEncryptedHookUrl']

# The Slack channel to send a message to stored in the slackChannel environment variable
SLACK_CHANNEL = os.environ['slackChannel']

HOOK_URL = boto3.client('kms').decrypt(CiphertextBlob=b64decode(ENCRYPTED_HOOK_URL))['Plaintext'].decode('utf-8')

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


def lambda_handler(event, context):
    logger.info("Event: " + str(event))
    message = (event['detail'])
    logger.info("Message: " + str(message))

    alarm_name = message['alarmName']
    old_state = message['previousState']['value']
    new_state = message['state']['value']
    reason = message['state']['reason']

    slack_message = {
        'channel': SLACK_CHANNEL,
        'text': "%s state is now %s: %s" % (alarm_name, new_state, reason)
    }
    logger.info(HOOK_URL);
    req = Request(HOOK_URL, json.dumps(slack_message).encode('utf-8'))
    try:
        response = urlopen(req)
        response.read()
        logger.info("Message posted to %s", slack_message['channel'])
    except HTTPError as e:
        logger.error("Request failed: %d %s", e.code, e.reason)
    except URLError as e:
        logger.error("Server connection failed: %s", e.reason)

event.json

{
    "version": "0",
    "id": "c4c1c1c9-6542-e61b-6ef0-8c4d36933a92",
    "detail-type": "CloudWatch Alarm State Change",
    "source": "aws.cloudwatch",
    "account": "123456789012",
    "time": "2019-10-02T17:04:40Z",
    "region": "us-east-1",
    "resources": [
        "arn:aws:cloudwatch:us-east-1:123456789012:alarm:ServerCpuTooHigh"
    ],
    "detail": {
        "alarmName": "ServerCpuTooHigh",
        "configuration": {
            "description": "Goes into alarm when server CPU utilization is too high!",
            "metrics": [
                {
                    "id": "30b6c6b2-a864-43a2-4877-c09a1afc3b87",
                    "metricStat": {
                        "metric": {
                            "dimensions": {
                                "InstanceId": "i-12345678901234567"
                            },
                            "name": "CPUUtilization",
                            "namespace": "AWS/EC2"
                        },
                        "period": 300,
                        "stat": "Average"
                    },
                    "returnData": true
                }
            ]
        },
        "previousState": {
            "reason": "Threshold Crossed: 1 out of the last 1 datapoints [0.0666851903306472 (01/10/19 13:46:00)] was not greater than the threshold (50.0) (minimum 1 datapoint for ALARM -> OK transition).",
            "reasonData": "{\"version\":\"1.0\",\"queryDate\":\"2019-10-01T13:56:40.985+0000\",\"startDate\":\"2019-10-01T13:46:00.000+0000\",\"statistic\":\"Average\",\"period\":300,\"recentDatapoints\":[0.0666851903306472],\"threshold\":50.0}",
            "timestamp": "2019-10-01T13:56:40.987+0000",
            "value": "OK"
        },
        "state": {
            "reason": "Threshold Crossed: 1 out of the last 1 datapoints [99.50160229693434 (02/10/19 16:59:00)] was greater than the threshold (50.0) (minimum 1 datapoint for OK -> ALARM transition).",
            "reasonData": "{\"version\":\"1.0\",\"queryDate\":\"2019-10-02T17:04:40.985+0000\",\"startDate\":\"2019-10-02T16:59:00.000+0000\",\"statistic\":\"Average\",\"period\":300,\"recentDatapoints\":[99.50160229693434],\"threshold\":50.0}",
            "timestamp": "2019-10-02T17:04:40.989+0000",
            "value": "ALARM"
        }
    }
}