Why I am getting blank response from the AWS lambda function even though AWS lambda test works properly?

Description

---

I am creating an intermediary service between my frontend and my backend using AWS lambda function. The job of the function is to take the payload from the UI and send to the backend, if Backend is live then send the 200 status (progress of ML model, short pooling). Suppose the backend is not live and the backend pod is restarting use the previous JSON saved inside a response.json file and return that back to the frontend until the pod is restarted and live to serve. Here is my lambda function.

---

My AWS Lambda code

import json
import os
import requests

def save_json_file_to_tmp(response_payload, filename="response.json"):
    tmp_dir = "/tmp"
    tmp_file_path = os.path.join(tmp_dir, filename)
    with open(tmp_file_path, "w") as f:
        json.dump(response_payload, f)

def read_json_file(filename="response.json"):
    tmp_dir = "/tmp"
    tmp_file_path = os.path.join(tmp_dir, filename)
    with open(filename, "r") as f:
        # Load the JSON payload.
        response_payload = json.load(f)

    return response_payload

def lambda_handler(event, context):
    """Forwards a POST request to another service and redirects back to the first microservice.

    Args:
        event: The Lambda event.
        context: The Lambda context.

    Returns:
        A JSON response object.
    """
    
    print(event)
    print(type(event))
    print("=========================================================")

    # Get the request data from the event.
    
    try:
        request_data = json.loads(event["body"])
    except KeyError as e:
        request_data = event

    # Get the destination URL from the request data.
    dest_url = request_data["dest_url"]

    # Forward the POST request to the destination service.
    response = requests.post(dest_url, json=request_data)

    # Check the response status code.
    if response.status_code == 200:
        # Get the response payload.
        response_payload = json.loads(response.content)
        print("++++++++++++++++++++++++++++++++++")
        print(response_payload)
        print("++++++++++++++++++++++++++++++++++")
        # Save the response payload to a temporary file.
        save_json_file_to_tmp(response_payload)

        # Redirect back to the first microservice with the response payload.
        return {
            "statusCode": 200,
            "body": json.dumps(response_payload),
            "headers": {
                "Content-Type": "application/json"
            }
        }
    elif response.status_code == 502:
        # Read the response payload from the temporary file.
        response_payload = read_json_file_to_tmp()

        # Redirect back to the first microservice with the response payload.
        return {
            "statusCode": 200,
            "body": json.dumps(response_payload),
            "headers": {
                "Content-Type": "application/json"
            }
        }
    else:
        # Return an error response.
        return {
            "statusCode": 500,
            "body": json.dumps({
                "error": "Unexpected response from destination service."
            }),
            "headers": {
                "Content-Type": "application/json"
            }
        }

---

Now to test the lambda I created a test event checkLiveOrNot

{
  "app": "my_app",
  "session_id": "3432428374827347234",
  "table": "progress",
  "user_id": "myaccount@gmail.cm",
  "flag": false,
  "project_name": "mybig1gbproject",
  "user_name": "john doe",
  "file_name": "",
  "fit_progress": 0,
  "model_fit": 0,
  "total_fit": 0,
  "model_calc": 0,
  "total_calc": 0,
  "calc_progress": 0,
  "model_arch": "lambda",
  "dest_url": "https://mybackendservice/api/maincore/progress"
}

and invoked and it returned me the proper output in the lambda test console.

Test Event Name
checkLiveOrNot

Response
{
  "statusCode": 200,
  "body": "{\"_id\": \"34347tyi738483h8d73h\", \"session_id\": \"3432428374827347234\", \"data\": 0, \"model_no\": 0, \"table\": \"progress\", \"total_fit\": 1, \"total_calc\": 1, \"orc_fail\": 0, \"model_progress\": 0.0, \"current_model\": 0, \"model_progress\": 100.0, \"current_calc\": 1}",
  "headers": {
    "Content-Type": "application/json"
  }
}

Function Logs
START RequestId: 0d820ce34rtry9-2e11-420dsdfa-961e-c4434515b18f Version: $LATEST
{'app': 'my-app', 'session_id': '34347tyi738483h8d73h', 'table': 'progress', 'user_id': 'danish.xavier@iqvia.com', 's3_flag': False, 'project_name': 'checksampleforapitesting', 'user_name': 'danish.xavier', 'file_name': '', 'model_fit_progress': 0, 'current_model_fit': 0, 'total_model_fit': 0, 'current_model_calc': 0, 'total_model_calc': 0, 'model_calc_progress': 0, 'model_arch': 'eks', 'dest_url': 'https://promo-internal-promo-usv-demotemp-env.mmx.mco.solutions.iqvia.com/api/core/progress_lambda'}
<class 'dict'>
=========================================================
++++++++++++++++++++++++++++++++++
{'_id': '34347tyi738483h8d73h', 'session_id': '34347tyi738483h8d73h', 'data': 0, 'model_no': 0, 'table': 'progress', 'total_fit': 1, 'total_calc': 1, 'orc_fail': 0, 'model_progress': 0.0, 'current_model': 0, 'model_progress': 100.0, 'current_calc': 1}
++++++++++++++++++++++++++++++++++
END RequestId: 0d820ce9-2e11-420a-961e-c4434515b18f
REPORT RequestId: 0d82dfdf0ce9-2dfdfe11-42dfdf0a-961e-c44345dfdf15b18f  Duration: 281.79 ms Billed Duration: 282 ms Memory Size: 128 MB Max Memory Used: 54 MB  Init Duration: 324.60 ms

Request ID
0d820ce9-2e11-420a-961e-c4434515b18f

Now when I sent a POST request to this lambda via postman with the same payload I am getting 200 Response but showing nothing on the Postman screen. I tried using python and sent request. here is the code.

---

import json
import requests

# Create the request headers
headers = {
    'Content-Type': 'application/json'
}

# Create the request body
payload = {
  "app": "my_app",
  "session_id": "3432428374827347234",
  "table": "progress",
  "user_id": "myaccount@gmail.cm",
  "flag": false,
  "project_name": "mybig1gbproject",
  "user_name": "john doe",
  "file_name": "",
  "fit_progress": 0,
  "model_fit": 0,
  "total_fit": 0,
  "model_calc": 0,
  "total_calc": 0,
  "calc_progress": 0,
  "model_arch": "lambda",
  "dest_url": "https://mybackendservice/api/maincore/progress"
}

# Send the POST request
response = requests.post(
    'https://8973043wa7lrta.execute-api.us-east-1.amazonaws.com/dev/progress_lambda',
    headers=headers,
    json=payload
)

# Check the response status code
if response.status_code == 200:
    # The request was successful
    print('Request successful')

    # Get the response payload
    response_payload = response.content

    print(response_payload)

The Output from the program:

Request successful
b''

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