CODEWITHSUNDEEP
pythonamazon-web-servicesaws-lambda
MountainBiker
MountainBiker

Reputation: 411

Invoking child lambda function from parent lambda function - parent lambda returning empty string

I have a child lambda function which I can invoke successfully from the parent and get a 200 status code but the parent lambda gets an empty string despite the fact the the child lambda is returning the expected data. I am fairly new to python, so I am sure it is something simple that I'm missing.

Child Lambda

# empty data dict as this can change in the function due to various conditions
data{}

# populate data dict for returned payload
                data["first_string"] = 'first'
                data["second_string"] = 'second'
                data["first_number"] = 100

# this is what the child lambda returns and what expect to get when I invoke from the parent lambda
return json.dumps(data)

Child lambda output is as expected. See below.

"{\"first_string\": \"first\", \"second_string\": \"second\", \"first_number\": 100}"

Parent lambda

response = Lambda_client.invoke(
            FunctionName='lambda-function-arn',
            InvocationType='RequestResponse',
            Payload=json.dumps(input_params),
            LogType='Tail'
        )

response_payload = response['Payload'].read().decode("utf-8")
print("This is the response from the child lambda" + response_payload)

Parent lambda response_payload is an empty string. When I print it (as above) I get...

This is the response from the child lambda"{}"

It should contain the output from the child lambda. Can anyone tell me what I'm doing wrong?

Upvotes: 0

Views: 1482

Answers (1)

Цветан Иванов
Цветан Иванов

Reputation: 1161

Everything in your code is working correctly. I have created two Python 3.9 lambda functions. And the parent lambda is getting the correct response.

Things to try:

  1. Check that the ARN of the child lambda doesn't have an old version that returns "{}". And that you are not invoking that version. (https://docs.aws.amazon.com/lambda/latest/dg/configuration-versions.html)
  2. Check that you are not emptying the dict depending on some input values
  3. Create two new lambdas and try copying my code directly

parent lambda

import json
import boto3

Lambda_client = boto3.client('lambda')

def lambda_handler(event, context):
    inputParams = {}
 
    response = Lambda_client.invoke(
                FunctionName='arn',
                InvocationType='RequestResponse',
                Payload=json.dumps(inputParams),
                LogType='Tail'
            )
    
    print(response)
    response_payload = response['Payload'].read().decode("utf-8")
    print("This is the response from the child lambda" + response_payload)

    return {
        'statusCode': 200,
        'body': json.dumps('This is the parent lambda')
    }

child lambda

import json

def lambda_handler(event, context):
    data = {}
    
    data["first_string"] = 'first'
    data["second_string"] = 'second'
    data["first_number"] = 100

    return json.dumps(data)

Upvotes: 2

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