Package fast api dependencies as lambda layer not works

[CGarces]

Hi!

I having some issues trying to run aws-lambda-web-adapter projects with a common layer with all the fast API dependencies.

Template for lambda layer:

  FastApiLayer:
    Type: AWS::Serverless::LayerVersion
    Properties:
      ContentUri: FastApiLayer/
      CompatibleRuntimes:
        - python3.11
    Metadata:
      BuildMethod: python3.11
      BuildArchitecture: x86_64

Template for lambda function:

  FlaskFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: app/
      Handler: run.sh
      Runtime: python3.11
      MemorySize: 128
      Environment:
        Variables:
          AWS_LAMBDA_EXEC_WRAPPER: /opt/bootstrap
          PORT: 8000
      Layers:
        - !Sub arn:aws:lambda:${AWS::Region}:753240598075:layer:LambdaAdapterLayerX86:20
        - Fn::ImportValue: "backend-layers-FastApiLayer"

requirements.txt for lambda layer

fastapi~=0.109.2
uvicorn[standard]==0.27.1
pydantic==2.6.1

And finally the run.sh

#!/bin/bash
exec python -m uvicorn --port=$PORT app:app

I get the following error /var/lang/bin/python: No module named uvicorn

Something is different in the way that SAM deploy the package with and without the lambda layer.

I have unziped the layer, and the original function (with the dependencies, not the layer) and I can't see the diff except for the folder structure.
The layer package all the dependencies at "/python/" folder, that according to the documentation, is de correct way.

original funcion:

• root
  • my code
  • uvicorn
  • uvicorn-0.27.1.dist-info

Lambda layer:

• root
  • python/
    • uvicorn
    • uvicorn-0.27.1.dist-info

Y need to change anything in the run.sh file to work with uvicorn inside a lambda layer?

[bnusunny]

Check out the run.sh in fastapi-zip example. You need to configure a few environment variables.

[CGarces]

/opt/python must to be added to PYTHONPATH

#!/bin/bash
PATH=$PATH:$LAMBDA_TASK_ROOT/bin PYTHONPATH=$LAMBDA_TASK_ROOT:/opt/python exec python -m uvicorn --port=$PORT app:app