AWS Lambda - cloudwatch-alarm-to-slack-python blueprint extended

lambda_function.py

'''
Follow these steps to configure the webhook in Slack:

  1. Navigate to https://<your-team-domain>.slack.com/services/new

  2. Search for and select "Incoming WebHooks".

  3. Choose the default channel where messages will be sent and click "Add Incoming WebHooks Integration".

  4. Copy the webhook URL from the setup instructions and use it in the next section.

To encrypt your secrets use the following steps:

  1. Create or use an existing KMS Key - http://docs.aws.amazon.com/kms/latest/developerguide/create-keys.html

  2. Expand "Encryption configuration" and click the "Enable helpers for encryption in transit" checkbox

  3. Paste <SLACK_CHANNEL> into the slackChannel environment variable

  Note: The Slack channel does not contain private info, so do NOT click encrypt

  4. Paste <SLACK_HOOK_URL> into the kmsEncryptedHookUrl environment variable and click "Encrypt"

  Note: You must exclude the protocol from the URL (e.g. "hooks.slack.com/services/abc123").

  5. Give your function's role permission for the `kms:Decrypt` action using the provided policy template
  
To Customise:

  1. You can edit the blocks as you see fit. 

  2. Modify the state_emoji values with any emojis in your Slack instance (this includes custom emojis)
'''

import boto3
import json
import logging
import os

from base64 import b64decode
from urllib.request import Request, urlopen
from urllib.error import URLError, HTTPError
  
def _finditem(obj, key):
    if key in obj: return obj[key]
    for k, v in obj.items():
        if isinstance(v,dict):
            item = _finditem(v, key)
            if item is not None:
                return item
        elif isinstance(v, list):
            for i in v:
                item = _finditem(i, key)
                if item is not None:
                    return item

# 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 = "https://" + boto3.client('kms').decrypt(
    CiphertextBlob=b64decode(ENCRYPTED_HOOK_URL),
    EncryptionContext={'LambdaFunctionName': os.environ['AWS_LAMBDA_FUNCTION_NAME']}
)['Plaintext'].decode('utf-8')

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']
    alarm_title = message['AlarmDescription']
    old_state = message['OldStateValue']
    new_state = message['NewStateValue']
    reason = message['NewStateReason']
    metric_name = _finditem(message, 'MetricName')
    namespace = _finditem(message, 'Namespace')
    dimensions = _finditem(message, 'Dimensions')
    

        
    
    state_emoji = {
        'ALARM': 'alert',
        'OK': 'heavy_check_mark'
    }

    slack_message = {
        'channel': SLACK_CHANNEL,
        'icon_emoji': ":aws:",
        'blocks': [
            {
                'type': "section",
                "text": {
                    "type": "mrkdwn",
                    "text": ":%s: *%s* :%s:" % (state_emoji[new_state], alarm_title, state_emoji[new_state])
                }
            },
            {
                "type": "section",
                "fields": [
                    {
                        "type": "mrkdwn",
                        "text": "*New State:*\n*%s*" % (new_state)
                    },
                    {
                        "type": "mrkdwn",
                        "text": "*Old State:*\n%s" % (old_state)
                    },
                    {
                        "type": "mrkdwn",
                        "text": "*Service :*\n%s" % (namespace)
                    },
                    {
                        "type": "mrkdwn",
                        "text": "*Region:*\n%s" % (message['Region'])
                    },
                    {
                        "type": "mrkdwn",
                        "text": "*Metric:*\n%s" % (metric_name)
                    },
                    {
                        "type": "mrkdwn",
                        "text": "*Threshold:*\n%s" % (_finditem(message, 'Threshold'))
                    },
                    {
                        "type": "mrkdwn",
                        "text": "*Timestamp:*\n%s" % (message['StateChangeTime'])
                    }
                ]
            },
            {
                "type": "divider"
            },
            {
                'type': "section",
                "text": {
				    "type": "mrkdwn",
				    "text": "*Dimensions:*"
				},
                'fields': []
            },
            {
                "type": "divider"
            },
            {
                "type": "section",
			    "text": {
				    "type": "mrkdwn",
				    "text": "*Details:*\n%s*" % (reason)
				}
            }
        ]
        
    }
    
    if dimensions is not None:
        for d in dimensions:
            slack_message['blocks'][3]['fields'].append({
                "type": "mrkdwn",
                "text": "*%s:*\n%s" % (d['name'],d['value'])
            })

    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 (%s) failed: %s", HOOK_URL, e.reason)