ModuleNotFoundError in Lambda after Redeployment without Configuration Changes

Question

### Description
I am experiencing a `ModuleNotFoundError` when executing an AWS Lambda function. The error implies that the Lambda runtime cannot locate or recognize the handler module as a Python package. Notably, this issue appeared after redeploying the function without any modifications to the previously working path or configuration.

### Error Details
- **Timestamp**: 2024-05-13T12:24:28.530Z
- **File**: `/opt/.../exec_wrapper.py`
- **Error Message**:
  ```
  [ERROR] Runtime.ImportModuleError: Unable to import module 'app/agents/mainAgent/lambda_function.handler': No module named 'app.agents'; 'app' is not a package
  Traceback (most recent call last):
  ...
  ModuleNotFoundError: No module named 'app.agents'; 'app' is not a package
  ```
Serverless.yml
```yaml
mainAgent:
    description: Handle various type of text requests
    role: platformMainAgentRole
    handler: app/agents/mainAgent/lambda_function.handler
    architecture: arm64
    timeout: 60
    runtime: python3.9
  events:
      - schedule:
          rate: ${self:custom.rates.${self:provider.stage}}
          enabled: true
          inputTransformer:
            inputTemplate: '{}'
    layers:
      - { Ref: OpenaiLambdaLayer }
      - { Ref: TiktokenLambdaLayer }
```
### Expected Behavior
The function should be able to find and import the handler module as it did before the redeployment, without any issues.

### Actual Behavior
The function fails to start, throwing an error that it cannot find the specified module. This is puzzling as there were no changes in the Lambda's configuration or handler path that had previously been functional.

### Steps to Reproduce
1. Setup the Lambda function with the handler path specified as `app/agents/mainAgent/lambda_function.handler`.
2. Deploy the function using the typical deployment process.
3. Attempt to invoke the function, triggering the error.

### Additional Information
The sudden appearance of this issue in a stable setup raises concerns about potential changes or inconsistencies in the Lambda environment or deployment processes. Any insights or similar experiences shared by the community could help in pinpointing and resolving this issue.

Hideki_M · Answer

Hi,

I'll share my valid Lambda definition from the SAM YAML file.

* Target code: **./src/api/create_order.py**

```bash-session
src
├── api
│   ├── __init__.py
│   ├── create_order.py
└── layers
   └── utils.py
```

```yaml
  ### Integrates the 🟠Lambda function
  AddOrderFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: src/api
      Handler: create_order.lambda_handler
      Runtime: python3.9
      Tracing: Active
      Policies:
        - DynamoDBCrudPolicy:
            TableName: !Ref OrdersTable
      Environment:
        Variables:
          TABLE_NAME: !Ref OrdersTable
      Events:
        ApiEvent:
          Type: Api
          Properties:
            Path: /orders
            Method: post
            RestApiId: !Ref WorkshopApiGateway
```

|Key point of properties||
|---|---|
|`CodeUri`| The local path to the function |
||e.g., src/api (the path from current directory)|
|`Handler`|The function within your code that is called to begin execution.|
||e.g., __FILE_NAME__(without .py)**.lambda_handler** (Not **lambda_function.handler**)|

Note: 
[**AWS SAM template anatomy**](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-specification-template-anatomy.html)

I hope this helps!

ModuleNotFoundError in Lambda after Redeployment without Configuration Changes

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Actual Behavior

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Additional Information

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Key point of properties
`CodeUri`	The local path to the function
	e.g., src/api (the path from current directory)
`Handler`	The function within your code that is called to begin execution.
	e.g., FILE_NAME(without .py).lambda_handler (Not lambda_function.handler)