AWS SAM API endpoint using a Lambda is throwing error when it runs locally with "sam start local-api"

Question

I am building a simple API endpoint using AWS Lambda function and API Gateway. I am orchestrating those resources using SAM. I can deploy my function to the AWS cloud and access the endpoint. It's working as expected.

Here is my lambda function.

exports.lambdaHandler  = async (event) => ({
    statusCode: 200,
    body: {
        message: `Hello World!`
    }
})

Here is my SAM CloudFormation template

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: HTTP API

Globals:
  Function:
    Timeout: 5
    Handler: app.lambdaHandler
    Runtime: nodejs16.x

Resources:
  LambdaFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: src/
      Events:
        Api:
          Type: Api
          Properties:
            Path: /
            Method: GET

Outputs:
  WebEndpoint:
    Description: "API Gateway endpoint URL for Prod stage"
    Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/"

But I am getting the error when I run the endpoint locally in the Docker container. I run the following command to run the API locally.

sam build --use-container && sam local start-api

When I run that, the docker image was build successfully and there is no error in the console. In the console, it gives me a local endpoint, http://127.0.0.1:3000/.

When I visit the endpoint in the browser, I am getting this response.

{"message":"Internal server error"}

I also seeing the following errors in the console.

Invoking app.lambdaHandler (nodejs16.x)
Image was not found.
Removing rapid images for repo public.ecr.aws/sam/emulation-nodejs16.x
Building image........................
Failed to build Docker Image
NoneType: None
Exception on / [GET]
Traceback (most recent call last):
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/flask/app.py", line 2073, in wsgi_app
    response = self.full_dispatch_request()
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/flask/app.py", line 1518, in full_dispatch_request
    rv = self.handle_user_exception(e)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/flask/app.py", line 1516, in full_dispatch_request
    rv = self.dispatch_request()
         ^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/flask/app.py", line 1502, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/local/apigw/local_apigw_service.py", line 361, in _request_handler
    self.lambda_runner.invoke(route.function_name, event, stdout=stdout_stream_writer, stderr=self.stderr)
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/commands/local/lib/local_lambda.py", line 137, in invoke
    self.local_runtime.invoke(
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/lib/telemetry/metric.py", line 315, in wrapped_func
    return_value = func(*args, **kwargs)
                   ^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/local/lambdafn/runtime.py", line 177, in invoke
    container = self.create(function_config, debug_context, container_host, container_host_interface)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/local/lambdafn/runtime.py", line 73, in create
    container = LambdaContainer(
                ^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/local/docker/lambda_container.py", line 93, in __init__
    image = LambdaContainer._get_image(
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/local/docker/lambda_container.py", line 236, in _get_image
    return lambda_image.build(runtime, packagetype, image, layers, architecture, function_name=function_name)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/local/docker/lambda_image.py", line 164, in build
    self._build_image(
  File "/opt/homebrew/Cellar/aws-sam-cli/1.70.0/libexec/lib/python3.11/site-packages/samcli/local/docker/lambda_image.py", line 279, in _build_image
    raise ImageBuildException("Error building docker image: {}".format(log["error"]))
samcli.commands.local.cli_common.user_exceptions.ImageBuildException: Error building docker image: The command '/bin/sh -c mv /var/rapid/aws-lambda-rie-x86_64 /var/rapid/aws-lambda-rie && chmod +x /var/rapid/aws-lambda-rie' returned a non-zero code: 1
2023-01-21 09:29:27 127.0.0.1 - - [21/Jan/2023 09:29:27] "GET / HTTP/1.1" 502 -
2023-01-21 09:29:27 127.0.0.1 - - [21/Jan/2023 09:29:27] "GET /favicon.ico HTTP/1.1" 403 -

What is wrong with my code and how can I fix it?

Answer 1

We had a similar problem only on MacOS so if you are using MacOS this might help you (there is homebrew in your error response so i guess you are) In our case aws-sam-cli was installed via brew.

What we did was deleting aws-sam-cli and installed it via Command Line - All users using arm64.pkg

https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/install-sam-cli.html

After that we got

=== ERROR: Error: Protocol error (Target.setDiscoverTargets): Target closed.

but this might be related to our project only.