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I've got a Python application that connects to a database and I would like the db credentials to be different when it's running in local env (for testing) or within a lambda function (for production).

Is there any way, from the Python app, to detect that it is running inside the lambda function?

laurent
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5 Answers5

28

This works for me

os.environ.get("AWS_EXECUTION_ENV") is not None

EDIT: I find the existence of the context object insufficient for such a check because you might be mocking it when not running within an AWS lambda function. Then again, you may be mocking the AWS_EXECUTION_ENV as well ...

Nikolay Manolov
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5

EDIT 2: With the introduction of Lambda function custom runtimes, it may be better to check for the AWS_LAMBDA_FUNCTION_NAME environment variable, like so:

os.environ.get("AWS_LAMBDA_FUNCTION_NAME") is not None

EDIT: See the other answer, this is a better solution:

os.environ.get("AWS_EXECUTION_ENV") is not None

Original answer:

How about checking for the existence of the context object in the handler function? http://docs.aws.amazon.com/lambda/latest/dg/python-programming-model-handler-types.html

Mark B
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    That only works in the handler function. Would be nice to know globally. – Jason Mar 30 '17 at 23:56
  • the `AWS_REGION` env would be set – Jonathan Mar 12 '18 at 10:05
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    @Jonathan the `AWS_REGION` environment would also be set locally if you are using environment variables to configure the AWS CLI/SDK, so I don't think that's a good one to use here. `AWS_EXECUTION_ENV` seems more appropriate. – Mark B Dec 11 '20 at 13:44
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    Checking for context object doesn't work for library code. AWS_EXECUTION_ENV seems promising. – Chris Wolf Aug 06 '21 at 00:32
  • According to AWS documentation: "the AWS_EXECUTION_ENV environment variable is not defined for custom runtimes (for example, runtimes that use the provided or provided.al2 identifiers)." I think that AWS_LAMBDA_FUNCTION_NAME might be more suitable since it is always inserted – Yoni Melki Jun 02 '22 at 12:52
  • @YoniMelki thank you, I don't think custom runtimes were available when I wrote this answer originally back in 2016. I've updated the answer with your input. – Mark B Jun 02 '22 at 13:38
1

For unit testing I use the structure:

+ my_function/
+- __init__.py - empty files
+- code/
   +- __init__.py
   +- lambda_function.py
+- unittest/
   +- __init__.py
   +- tests.py - from ..code.lambda_function import *

When running unit tests with python -m my_function.unittest.tests, in lambda_function.py the __name__ == 'my_function.code.lambda_function'.

When running in the Lambda running, __name__ == 'lambda_function'. Note that you'll get the same value if you run with python -m my_function.code.lambda_function so you'll always need a wrapper.

Jason
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0

This is what I use

import os

try:
  region = os.environ['AWS_REGION']
except:
  # Not in Lambda environment
  region = "us-east-1"
Jonathan
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-2

Because of this bug it is possible to tell if you are running inside an AWS Lambda Function.

import multiprocessing

def on_lambda():
    try:
        multiprocessing.Pool()
        on_lambda = False
    except:
        on_lambda = True
    return on_lambda

I used this to implement context sensible metric reporting successfully. Lets hope they don't fix the bug any soon!

pointtonull
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