AWS Lambda function, secret manager cannot get secret value

Question

I have created a lambda function to send billing reports to certain email addresses, for that im using my email address and app password. I have saved the app password under secret manager as other api. When i try to retrieve it using the lambda function it shows error.

import boto3
import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
import ast
import os
import datetime
import base64
import logging
import collections
import json

logger = logging.getLogger()
logger.setLevel(logging.INFO)


def get_secret():

    secret_name = "email_app_password"
    region_name = "ca-central-1"

    # Create a Secrets Manager client
    session = boto3.session.Session()
    client = session.client(
        service_name='secretsmanager',
        region_name=region_name
    )

    # In this sample we only handle the specific exceptions for the 'GetSecretValue' API.
    # See https://docs.aws.amazon.com/secretsmanager/latest/apireference/API_GetSecretValue.html
    # We rethrow the exception by default.

    try:
        get_secret_value_response = client.get_secret_value(
            SecretId=secret_name
        )
    except ClientError as e:
        if e.response['Error']['Code'] == 'DecryptionFailureException':
            # Secrets Manager can't decrypt the protected secret text using the provided KMS key.
            # Deal with the exception here, and/or rethrow at your discretion.
            raise e
        elif e.response['Error']['Code'] == 'InternalServiceErrorException':
            # An error occurred on the server side.
            # Deal with the exception here, and/or rethrow at your discretion.
            raise e
        elif e.response['Error']['Code'] == 'InvalidParameterException':
            # You provided an invalid value for a parameter.
            # Deal with the exception here, and/or rethrow at your discretion.
            raise e
        elif e.response['Error']['Code'] == 'InvalidRequestException':
            # You provided a parameter value that is not valid for the current state of the resource.
            # Deal with the exception here, and/or rethrow at your discretion.
            raise e
        elif e.response['Error']['Code'] == 'ResourceNotFoundException':
            # We can't find the resource that you asked for.
            # Deal with the exception here, and/or rethrow at your discretion.
            raise e
    else:
        # Decrypts secret using the associated KMS key.
        # Depending on whether the secret is a string or binary, one of these fields will be populated.
        if 'SecretString' in get_secret_value_response:
            secret = get_secret_value_response['SecretString']
        else:
            decoded_binary_secret = base64.b64decode(get_secret_value_response['SecretBinary'])
            
    # Your code goes here. 


def send_email(email_body):
    """
    Sends email according to environment variables.
    :param email_body: Body of email.
    :return: None
    """
    msg = MIMEMultipart('alternative')
    email = os.environ['EMAIL_FROM']
    try:
        secret_value = get_secret()
        print(secret_value[os.environ['SECRET_KEY_NAME']])
    except Exception as e:
        logger.exception("Exception while trying to get password from Secrets Manager")
        return
    sec_key = os.environ['SECRET_KEY_NAME']
    password = ast.literal_eval(secret_value)[os.environ['SECRET_KEY_NAME']]
    msg['Subject'] = os.environ["EMAIL_SUBJECT"]
    msg['From'] = email
    you = os.environ['EMAIL_TO'].split(',')
    msg['To'] = ", ".join(you)
    body = email_body
    msg.attach(MIMEText(body, 'html'))
    try:
        smtpObj = smtplib.SMTP('smtp.gmail.com', 587)
        smtpObj.starttls()
        smtpObj.login(email, password)
        smtpObj.sendmail(email, you, msg.as_string())
        smtpObj.quit()
        logger.info('Email sent')
    except smtplib.SMTPException as e:
        logger.info("Error: unable to send email due to %s", e)


class FileOpener:
    """
    Class to cache file contents.
    """
    file_cache = {}

    @staticmethod
    def open_file(filename):
        if filename not in FileOpener.file_cache:
            with open(filename) as fp:
                FileOpener.file_cache[filename] = fp.read()
        return FileOpener.file_cache[filename]


def get_account_cost(account_no, start_day, end_day):
    client = boto3.client('ce')
    response = client.get_cost_and_usage(
        TimePeriod={
            'Start': start_day,
            'End': end_day
        },
        Granularity='MONTHLY',
        Filter={
            "And": [{
                "Dimensions": {
                    "Key": "LINKED_ACCOUNT",
                    "Values": [account_no]
                }
            }, {
                "Not": {
                    "Dimensions": {
                        "Key": "RECORD_TYPE",
                        "Values": ["Credit", "Refund"]
                    }
                }
            }]
        },
        Metrics=["BlendedCost"],
        GroupBy=[
            {
                'Type': 'DIMENSION',
                'Key': 'SERVICE'
            },
        ]
    )
    cost_dictionary = collections.Counter()
    for result in response['ResultsByTime']:
        for group in result['Groups']:
            servicename = group['Keys'][0]
            amount = round(float(group['Metrics']['BlendedCost']['Amount']), 2)
            if amount == 0.0:
                continue
            cost_dictionary[servicename] += amount
    return cost_dictionary


def combine_cost_dictionaries(prev_cost_dict, curr_cost_dict):
    combined_cost_dict = {}
    prev_cost_total = 0.0
    curr_cost_total = 0.0
    for service, curr_cost in curr_cost_dict.items():
        prev_cost = 0.0
        if service in prev_cost_dict:
            prev_cost = prev_cost_dict[service]
        combined_cost_dict[service] = (prev_cost, curr_cost)
        prev_cost_total += prev_cost
        curr_cost_total += curr_cost
    for service, prev_cost in prev_cost_dict.items():
        curr_cost = 0.0
        if service not in combined_cost_dict:
            combined_cost_dict[service] = (prev_cost, curr_cost)
            prev_cost_total += prev_cost
            curr_cost_total += curr_cost
    return combined_cost_dict, prev_cost_total, curr_cost_total


def generate_account_cost_html(account_name, combined_cost_dict, prev_cost_total, curr_cost_total):
    prev_date = str((datetime.datetime.now().date() - datetime.timedelta(days=2)))
    curr_date = str((datetime.datetime.now().date() - datetime.timedelta(days=1)))
    table_rows = ""
    sorted_combined_cost = sorted(combined_cost_dict.items(), key=lambda x: x[1][1], reverse=True)
    for service, costs in sorted_combined_cost:
        table_row = FileOpener.open_file("table_row.html")
        prev_cost = round(float(costs[0]), 2)
        curr_cost = round(float(costs[1]), 2)
        if prev_cost < 0.01:
            percentage_change = 'New Charge'
        else:
            percentage_change = ((curr_cost - prev_cost) / prev_cost) * 100
            percentage_change = round(float(percentage_change), 2)
            if percentage_change > 0:
                percentage_change = "↑ {}%".format(percentage_change)
            elif percentage_change == 0.0:
                percentage_change = "{}%".format(percentage_change)
            else:
                percentage_change = "↓ {}%".format(percentage_change)
        if percentage_change[0] == '↑':
            percentage_css = "background-color: pink;border:darkblue solid thin;"
        elif percentage_change == 'New Charge':
            percentage_css = "background-color: LightGreen;border:darkblue solid thin;"
        else:
            percentage_css = "border:lightblue solid thin;"
        table_rows += table_row.format(service, prev_cost, curr_cost, percentage_css, percentage_change)

    prev_cost_total = round(float(prev_cost_total), 2)
    curr_cost_total = round(float(curr_cost_total), 2)
    table = FileOpener.open_file("table.html")
    table = table.format(account_name, prev_cost_total, curr_cost_total, prev_date, curr_date, table_rows)
    return table


def lambda_handler(event, context):
    account_names = os.environ['ACCOUNT_NAMES'].split(",")
    account_numbers = os.environ['ACCOUNT_NUMBERS'].split(",")
    table_body_html = ''
    for account_name, account_no in zip(account_names, account_numbers):
        day_1 = str((datetime.datetime.now().date() - datetime.timedelta(days=2)))
        day_2 = str((datetime.datetime.now().date() - datetime.timedelta(days=1)))
        day_3 = str(datetime.datetime.now().date())
        prev_cost_dict = get_account_cost(account_no, day_1, day_2)
        curr_cost_dict = get_account_cost(account_no, day_2, day_3)
        combined_cost_dict, prev_cost_total, curr_cost_total = combine_cost_dictionaries(prev_cost_dict, curr_cost_dict)
        table_body = generate_account_cost_html(account_name, combined_cost_dict, prev_cost_total, curr_cost_total)
        table_body_html += table_body
    email_body = FileOpener.open_file("email_body.html").format(table_body_html)
    send_email(email_body)

I get the following error when running the lambda function. I have even tried removing the print line. Then the error goes to password = ast.literal_eval(secret_value)[os.environ['SECRET_KEY_NAME']]

[ERROR] 2022-08-18T06:02:03.968Z    2ae88ceb-39a6-4feb-aa7c-2cbb17ec655c    Exception while trying to get password from Secrets Manager
Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 88, in send_email
    print(secret_value[os.environ['SECRET_KEY_NAME']])
TypeError: 'NoneType' object is not subscriptableEND RequestId: 2ae88ceb-39a6-4feb-aa7c-2cbb17ec655c

Answer 1

Your get_secret function does not return the value to the calling code. Please edit the else clause:

    else:
        # Decrypts secret using the associated KMS key.
        # Depending on whether the secret is a string or binary, one of these fields will be populated.
        if 'SecretString' in get_secret_value_response:
            return get_secret_value_response['SecretString']
        else:
            return base64.b64decode(get_secret_value_response['SecretBinary'])