Lambda Python and Boto3 - Passing Exception

Question

I am now getting to the end of resolving a lambda exception issue. After getting some help debugging the recent exceptions and resolving them, there is one i cannot resolve, so would like to pass it.

import boto3

sts_client = boto3.client('sts')
assumed_role_object=sts_client.assume_role(
    RoleArn="arn:aws:iam::11111111:role/role",
    RoleSessionName="AssumedRoleSession2"
)
credentials=assumed_role_object['Credentials']

def lambda_handler(context,event):
    client                  = boto3.client(
        'iam',
        aws_access_key_id=credentials['AccessKeyId'],
        aws_secret_access_key=credentials['SecretAccessKey'],
        aws_session_token=credentials['SessionToken'],
    )
    sns                     = boto3.client('sns')
    response                = client.list_users()
    userVirtualMfa          = client.list_virtual_mfa_devices()
    mfaNotEnabled           = []
    virtualEnabled          = []
    physicalString          = ''

    # loop through virtual mfa to find users that actually have it
    for virtual in userVirtualMfa['VirtualMFADevices']:
        if 'User' not in virtual or 'UserName' not in virtual['User']:
     # Catch the exception
           raise Exception("Invalid virtual %s" % virtual)

        virtualEnabled.append(virtual['User']['UserName'])

    # loop through users to find physical MFA
    for user in response['Users']:
        userMfa  = client.list_mfa_devices(UserName=user['UserName'])

        if len(userMfa['MFADevices']) == 0:
            if user['UserName'] not in virtualEnabled:
                mfaNotEnabled.append(user['UserName']) 


    if len(mfaNotEnabled) > 0:
        physicalString = 'Physical & Virtual MFA is not enabled for the following users: \n\n' + '\n'.join(mfaNotEnabled)
    else:
        physicalString = 'All Users have Physical and Virtual MFA enabled'

    response = sns.publish(
        TopicArn='arn:aws:sns:eu-west-2:222222222:sns',
        Message= physicalString,
        Subject='Enable MFA',
    )

    return mfaNotEnabled

The exception is reporting correctly, but i would like the function to continue

Response:
{
  "stackTrace": [
    [
      "/var/task/lambda_mfa_function.py",
      27,
      "lambda_handler",
      "raise Exception(\"Invalid virtual %s\" % virtual)"
    ]
  ],
  "errorType": "Exception",
  "errorMessage": "Invalid virtual {u'SerialNumber': 'arn:aws:iam::11111111:mfa/blah-mfa-device', u'EnableDate': datetime.datetime(2016, 05, 16, 01, 6, 35, tzinfo=tzlocal()), u'User': {u'PasswordLastUsed': datetime.datetime(2018, 5, 1, 02, 35, 27, tzinfo=tzlocal()), u'CreateDate': datetime.datetime(2014, 7, 17, 13, 43, 27, tzinfo=tzlocal()), u'UserId': '11111111', u'Arn': 'arn:aws:iam::11111111:blah'}}"
}

Request ID:
"c11a70c9-3a59-486a-9aa9-7286a0cb0b94"

Function Logs:
START RequestId: c11a70c9-3a59-486a-9aa9-7286a0cb0b94 Version: $LATEST
Invalid virtual {u'SerialNumber': 'arn:aws:iam::11111111:mfa/blah-mfa-device', u'EnableDate': datetime.datetime(2016, 11, 16, 22, 6, 35, tzinfo=tzlocal()), u'User': {u'PasswordLastUsed': datetime.datetime(2020, 5, 1, 14, 35, 27, tzinfo=tzlocal()), u'CreateDate': datetime.datetime(2015, 7, 17, 13, 43, 27, tzinfo=tzlocal()), u'UserId': '265742304136', u'Arn': 'arn:aws:iam::11111111:blah'}}: Exception
Traceback (most recent call last):
  File "/var/task/lambda_mfa_function.py", line 27, in lambda_handler
    raise Exception("Invalid virtual %s" % virtual)
Exception: Invalid virtual {u'SerialNumber': 'arn:aws:iam::11111111:mfa/blah-mfa-device', u'EnableDate': datetime.datetime(2014, 12, 12, 02, 6, 35, tzinfo=tzlocal()), u'User': {u'PasswordLastUsed': datetime.datetime(2016, 7, 2, 1, 15, 27, tzinfo=tzlocal()), u'CreateDate': datetime.datetime(2014, 2, 7, 3, 33, 17, tzinfo=tzlocal()), u'UserId': '11111111', u'Arn': 'arn:aws:iam::11111111:blah'}}

Its throwing a key error on the root MFA i expect due to the nature in which the root name is held

  File "/var/task/lambda_mfa_function.py", line 26, in lambda_handler
    virtualEnabled.append(virtual['User']['UserName'])
KeyError: 'UserName'

Addin an

except:
    pass

Is causing the lambda to fail. Can someone kindly point me into the right direction?

thanks Nick

If you want the function to continue, then don't raise an exception. — John Rotenstein
– John Rotenstein, Commented Jun 4, 2020 at 10:45

Nick Barton-Wells · Accepted Answer · 2020-06-04 10:50:27Z

1

This fixed it for me and was posted on an earlier question

userVirtualMfa = client.list_virtual_mfa_devices()
try:
    for virtual in userVirtualMfa['VirtualMFADevices']:
        virtualEnabled.append(virtual['User']['UserName'])
except:
    print("'UserName' is not a valid key")

answered Jun 4, 2020 at 10:50

Nick Barton-Wells

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