CODEWITHSUNDEEP
amazon-s3aws-lambdaaws-cliamazon-snslocalstack
StoneThrow
StoneThrow

Reputation: 6255

AWS / LocalStack: How to verify/debug (failure of) execution of Lambda?

I'm learning about AWS, and very outside my element, which is typically embedded software. I'm porting this question from Software Engineering after several days of no traction there.

Problem/question: in trying to set up a S3 bucket where file additions trigger a Lambda, how can one debug or trace the sequence of events from file addition to SNS notification to Lambda execution?

I'm trying to set up the following:

  1. Someone adds something to a S3 bucket
  2. The file addition triggers a Lambda which adds the file to a git repo (More specifically: the file addition triggers a SNS notification on a topic to which a Lambda is subscribed -- I felt this was "better" than the S3 bucket directly invoking the Lambda because of the decoupling)

I'm using the AWS CLI for everything, and for the immediate future, I am limited to using LocalStack to substitute for "real" AWS.

What I've done so far (simplified):

This is my "hello-world" Lambda function, naively cobbled together from here and here:

import json

def lambda_handler(event, context):
    print("Hello from Lambda!")
    return {
        'statusCode': 200,
        'body': json.dumps('Hello from Lambda!')
    }

This is my put-bucket-notification-configuration file:

{
    "TopicConfigurations": [
        {
            "TopicArn": "arn:aws:sns:us-east-1:000000000000:my-topic",
            "Events": [
                "s3:ObjectCreated:*"
            ]
        }
    ]
}

My problem is this: I'm not sure how to test success or failure of the "pipeline" I've tried to build from S3 Bucket to Lambda invocation.

(Please correct misunderstanding:) if I'm manually invoking a Lambda function, the "context of execution" is the shell from which I issue the AWS CLI request. But when the "context of execution" is the "pipeline" that I built from S3 Bucket to SNS notification to Lambda, I don't understand where the Lambda's print statement or return-status will be directed to. I.e. when I invoke the Lambda manually, my shell gets the return-status, and the print statement seems to get directed to the outfile I specify; e.g.:

$ aws lambda invoke --function-name first_lambda outfile.txt --endpoint-url=http://localhost:4574
{
    "StatusCode": 200
}

...but how can I test end-to-end functionality, or failure, between bucket object-creation to SNS notification to Lambda invocation since there's no outfile for prints to be directed to, and no "context" to which to return a status to?

Upvotes: 1

Views: 3396

Answers (1)

Mehdi Fracso
Mehdi Fracso

Reputation: 518

The output of your print statements would be clearly logged on AWS CloudWatch, also every error will be logged there.

So be sure to visit cloudwatch and check what is happening behind the scenes.

Docs: https://docs.aws.amazon.com/cli/latest/reference/cloudwatch/index.html

Upvotes: 2

Related Questions