[Lambda] e.g. Amazon SNS -> Lambda -> Slack

sns2slack.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

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']

SLACK_ICON_EMOJI = os.environ.get('slackIconEmoji', ':exclamation:')
SLACK_USERNAME = os.environ.get('slackUsername', 'incoming-webhook')

HOOK_URL = "https://" + 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))

    try:
        message = json.loads(event['Records'][0]['Sns']['Message'])
    except json.JSONDecodeError as e:
        logger.warning("JSONDecodeError: %s", str(e))
        message = event['Records'][0]['Sns']['Message']
    except Exception as e:
        logger.error("failed: %s", str(e))

    try:
        subject = json.loads(event['Records'][0]['Sns']['Subject'])
    except json.JSONDecodeError as e:
        logger.warning("JSONDecodeError: %s", str(e))
        subject = event['Records'][0]['Sns']['Subject']
    except Exception as e:
        logger.error("failed: %s", str(e))

    if len(message) > 0:
        message = "```" + str(message) + "```"
        if len(subject) > 0:
            message = subject + "\n" + message
        slack_message = {
            'channel': SLACK_CHANNEL,
            'icon_emoji': SLACK_ICON_EMOJI,
            'username': SLACK_USERNAME,
            'text': "%s" % (message)
        }
        logger.info("slack_message: " + str(slack_message))
        
        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)

Ref. cloudwatch-alarm-to-slack-python Lambda blueprint

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. Click the "Enable Encryption Helpers" 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.