AWS Lambda function to send Telegram messages when CloudWatch alarms trigger

lambda_function.py

# You need to give the Lambda the following permissions.
# Head to the Lambda page, and under Configuration > Permissions > Resource-based policy statements add a new policy statement:
#  - Select "AWS Service"
#  - On "Service", choose "Other"
#  - Statement ID: AlarmAction
#  - Principal: lambda.alarms.cloudwatch.amazonaws.com
#  - Source ARN: arn:aws:cloudwatch:us-east-1:YOUR_ACCOUNT_ID:alarm:*
#  - Action: lambda:InvokeFunction
#
# The same result can be achieved with `aws-cli`:
# ```
# aws lambda add-permission \
# --function-name YOUR_LAMBDA_NAME  \
# --statement-id AlarmAction \
# --action 'lambda:InvokeFunction' \
# --principal lambda.alarms.cloudwatch.amazonaws.com \
# --source-account YOUR_ACCOUNT_ID \
# --source-arn arn:aws:cloudwatch:us-east-1:YOUR_ACCOUNT_ID:alarm:*
# ```
#
# The resulting policy should look like:
# ```
# {
#   "Version": "2012-10-17",
#   "Id": "default",
#   "Statement": [
#     {
#       "Sid": "AlarmAction",
#       "Effect": "Allow",
#       "Principal": {
#         "Service": "lambda.alarms.cloudwatch.amazonaws.com"
#       },
#       "Action": "lambda:InvokeFunction",
#       "Resource": "arn:aws:lambda:us-east-1:YOUR_ACCOUNT_ID:function:YOUR_LAMBDA_NAME",
#       "Condition": {
#         "StringEquals": {
#           "AWS:SourceAccount": "YOUR_ACCOUNT_ID"
#         },
#         "ArnLike": {
#           "AWS:SourceArn": "arn:aws:cloudwatch:us-east-1:YOUR_ACCOUNT_ID:alarm:*"
#         }
#       }
#     }
#   ]
# }
# ```
#
# Make sure to replace `YOUR_ACCOUNT_ID` and `YOUR_LAMBDA_NAME` with your actual account ID and Lambda name where necessary.
#
# Also, make sure to configure the `TELEGRAM_BOT_TOKEN` and `TELEGRAM_CHAT_ID` environment variables in your Lambda.
#
# Relevant CloudWatch documentation and sample event sent to Lambda: https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/AlarmThatSendsEmail.html

import os
import requests
import json

# Set your Telegram Bot token and chat ID here (or use environment variables)
TELEGRAM_BOT_TOKEN = os.environ.get('TELEGRAM_BOT_TOKEN')
TELEGRAM_CHAT_ID = os.environ.get('TELEGRAM_CHAT_ID')

def send_telegram_message(message):
    """Send a message to the Telegram group."""
    url = f"https://api.telegram.org/bot{TELEGRAM_BOT_TOKEN}/sendMessage"
    data = {
        "chat_id": TELEGRAM_CHAT_ID,
        "text": message,
        "parse_mode": "Markdown"
    }
    response = requests.post(url, data=data)
    return response.json()

def lambda_handler(event, context):
    # Parse the CloudWatch alarm data
    alarm_data = event['alarmData']

    # Construct message based on the alarm data
    alarm_name = alarm_data['alarmName']
    alarm_state = alarm_data['state']['value']
    alarm_reason = alarm_data['state']['reason']
    metric_namespace = alarm_data['configuration']['metrics'][0]['metricStat']['metric']['namespace']
    instance_id = alarm_data['configuration']['metrics'][0]['metricStat']['metric']['dimensions'].get('InstanceId', 'Unknown')

    message = f"*[AWS]* 👀 Heads up! Alarm triggered: {alarm_name}\n"
    message += f"State: {alarm_state}\n"
    message += f"Reason: {alarm_reason}\n"
    message += f"Instance ID: {instance_id}"

    # Send the message
    response = send_telegram_message(message)
    return response