Import Module Error when building a Docker Container with Python for AWS Lambda

Question

I'm trying to build a Docker container that runs Python code on AWS Lambda. The build works fine, but when I test my code, I get the following error:

{"errorMessage": "Unable to import module 'function': No module named 'utils'", "errorType": "Runtime.ImportModuleError", "stackTrace": []}

I basically have two python scripts in my folder, function.py and utils.py, and I import some functions from utils.py and use them in function.py.

Locally, it all works fine, but when I build the Container and test it with the following curl command, I get the above error. Test curl command:

curl --request POST \
  --url http://localhost:9000/2015-03-31/functions/function/invocations \
  --header 'Content-Type: application/json' \
  --data '{"Input": 4}'

Here's my dockerfile:

FROM public.ecr.aws/lambda/python:3.7

WORKDIR /

COPY . .

COPY function.py ${LAMBDA_TASK_ROOT}

COPY requirements.txt .

RUN  pip3 install -r requirements.txt --target "${LAMBDA_TASK_ROOT}"

CMD [ "function.lambda_handler" ]

What I read in related Stackoverflow questions is to try importing the functions from utils.py in another way, I've tried changing from utils import * to from .utils import all, I changed the WORKDIR in my Dockerfile, and I put the utils file in a separate utils folder and tried importing this way: from utils.utils import *. I have also tried running the code in Python 3.8.

Here's my folder structure: Here's my folder structure

Does anyone know what I'm doing wrong?

What's ${LAMBDA_TASK_ROOT} ? Shouldn't you be copying utils.py there too? — Paolo
– Paolo, Commented Jul 4, 2022 at 19:02
The ${LAMBDA_TASK_ROOT} I got from the AWS tutorial here. I didn't try explicitly copying the utils.py before (I thought this would be included in COPY . .?), but I just tried it anyway and got the same error :/ — tom
– tom, Commented Jul 4, 2022 at 19:24
COPY . . would copy all files to the workdir directory, which is /, while you want to copy the file to ${LAMBDA_TASK_ROOT} — Paolo
– Paolo, Commented Jul 4, 2022 at 19:38
Got it, thank you! Getting new errors now, so at least that one seems to be solved :) — tom
– tom, Commented Jul 4, 2022 at 19:47

Paolo · Accepted Answer · 2022-07-04 19:58:09Z

2

The Dockerfile statement COPY . . copies all files to the working directory, which given your previous WORKDIR, is /.

To resolve the Python import issue, you need to move the Python module to the right directory:

COPY utils.py ${LAMBDA_TASK_ROOT}

answered Jul 4, 2022 at 19:58

Paolo

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