Question 18335 in Amazon Web Sevices Question posted in
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Why can't AWS Lambda receive SNS payload? – Amazon Web Sevices

I found articles how to send alerts from Amazon Prometheus to Microsoft Teams with AWS SNS & Lambda. I configured everything according to articles. When I send test payload in Lambda, everything is ok, Lambda sends a message. But when I send the same test payload with SNS, I receive an error in Lambda (look below). What is the problem with test payload or Lambda or SNS? SNS Subscription configured to Lambda correctly.

[ERROR] KeyError: 'alertname'
Traceback (most recent call last):
  File "/var/task/teams-alerting-lambda.py", line 18, in lambda_handler
    alertname = message['alertname']

I added ‘print(event)’ command. When sending payload in SNS i receive in Lambda logs:

{'Records': [{'EventSource': 'aws:sns', 'EventVersion': '1.0', 'EventSubscriptionArn': 'ARN', 
'Sns': {'Type': 'Notification', 'MessageId': '', 'TopicArn': 'ARN', 'Subject': None, 
'Message': '{n  "Records": [n    {n      
"Sns": {n        
"Message": "{\"alertname\": \"CPU_ALERT_333\", \"status\": \"firing\", \"host_name\": \"host1\", \"cloud_account_id\": \"1234567890\", \"cloud_region\": \"eu-west-1\", \"summary\": \"High CPU Load\", \"severity\": \"warning\"}"n      }n    }n  ]n}', 
'Timestamp': 'TIME', 'SignatureVersion': '1', 'Signature': '...', 'SigningCertUrl': 'URL', 'UnsubscribeUrl': 'URL', 'MessageAttributes': {}}}]}

Payload:

{
  "Records": [
    {
      "Sns": {
        "Message": "{"alertname": "CPU_Alert", "status": "firing", "host_name": "host1", "cloud_account_id": "1234567890", "cloud_region": "eu-west-1", "summary": "High CPU Load", "severity": "warning"}"
      }
    }
  ]
}

Part of Python code that is responsible for handling payload:

13 def lambda_handler(event, context):
14    logger.info("Event: " + str(event))
15    message = json.loads(event['Records'][0]['Sns']['Message'])
16    logger.info("Message: " + str(message))
17
18    alertname = message['alertname']
19    status = message['status']
Tags:

2

Answers


  1. 0

    The Message is a string like this:

    "{"alertname": "CPU_Alert", "status": "firing", "host_name": "host1", "cloud_account_id": "1234567890", "cloud_region": "eu-west-1", "summary": "High CPU Load", "severity": "warning"}"

    You need to decode the string into a dict.

    I.E. json.loads(thestring)

    > foo = "{"alertname": "CPU_Alert", "status": "firing", "host_name": "host1", "cloud_account_id": "1234567890", "cloud_region": "eu-west-1", "summary": "High CPU Load", "severity": "warning"}"
> foo
'{"alertname": "CPU_Alert", "status": "firing", "host_name": "host1", "cloud_account_id": "1234567890", "cloud_region": "eu-west-1", "summary": "High CPU Load", "severity": "warning"}'
> import json
> bar = json.loads(foo)
> bar['alertname']
'CPU_Alert'

    Catch the KeyError and see what you got:

    foo = "{"notalertname": "surprise"}"
try:
    message = json.loads(foo)
    alertname = message['alertname']
except KeyError:
    print(f"KeyError: {message.items()}")
    
KeyError: dict_items([('notalertname', 'surprise')])
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  2. 0

    You have to use ast python package on the event first to get the valid message, and then you can use json to get your alertname:

    import ast

def lambda_handler(event, context):
    logger.info("Event: " + str(event))

    records = ast.literal_eval(event['Records'][0]['Sns']['Message'])
    message = json.loads(records['Records'][0]['Sns']['Message'])
    logger.info("Message: " + str(message))

    alertname = message['alertname']
    status = message['status']

    p.s.
    May need to implement iteration over all event['Records'] in case you get more then one record from sns.

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