When I attempt to upload a function to my Localstack instance where the runtime is specified as `provided` aka custom runtime

https://docs.aws.amazon.com/lambda/latest/dg/runtimes-custom.html


> To use a custom runtime, set your function's runtime to provided.
> ...
> If there's a file named `bootstrap` in your deployment package, Lambda executes that file. If not, Lambda looks for a runtime in the function's layers. If the bootstrap file isn't found or isn't executable, your function returns an error upon invocation.


So here's what's happening, when I upload the function to Localstack I get a Boto error:

```
File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_starter.py", line 173, in parse_and_create_resource
localstack_1  |     return _parse_and_create_resource(logical_id, resource_json, resources_map, region_name)
localstack_1  |   File "/opt/code/localstack/localstack/services/cloudformation/cloudformation_starter.py", line 260, in _parse_and_create_resource
localstack_1  |     result = deploy_func(logical_id, resource_wrapped, stack_name=stack_name)
localstack_1  |   File "/opt/code/localstack/localstack/utils/cloudformation/template_deployer.py", line 715, in deploy_resource
localstack_1  |     result = deploy_resource_via_sdk_function(resource_id, resources, resource_type, func, stack_name)
localstack_1  |   File "/opt/code/localstack/localstack/utils/cloudformation/template_deployer.py", line 785, in deploy_resource_via_sdk_function
localstack_1  |     raise e
localstack_1  |   File "/opt/code/localstack/localstack/utils/cloudformation/template_deployer.py", line 782, in deploy_resource_via_sdk_function
localstack_1  |     result = function(**params)
localstack_1  |   File "/opt/code/localstack/.venv/lib/python3.7/site-packages/botocore/client.py", line 272, in _api_call
localstack_1  |     return self._make_api_call(operation_name, kwargs)
localstack_1  |   File "/opt/code/localstack/.venv/lib/python3.7/site-packages/botocore/client.py", line 576, in _make_api_call
localstack_1  |     raise error_class(parsed_response, operation_name)
localstack_1  | botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the CreateFunction operation: Unable to find handler script 
```

The last item in this stack trace is the issue:

> botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the CreateFunction operation: Unable to find handler script 

So it looks like it searching for `myHandler.sh` where it's appending that `.sh` or something is and that file doesn't exist so it's dying.

Per the amazon docs it should just be looking for a file name `bootstrap` if the lambda runtime is set to `provided`.

Now it's entirely possible this is an issue in Boto, but jumping to line **576** per the stack trace in the Boto source shows it's just emitting the http error, which leads me to think it's in Localstack .

**... Later ...**

Ok upon further inspection it looks like this if the offending line:

https://github.com/localstack/localstack/blob/master/localstack/services/awslambda/lambda_api.py#L420-L421

It's explicitly affixing that `.sh` extension. May AWS changed things around around how they handle "bootstrap" and at some point it in the past it was "bootstrap.sh" I dunno.. Regardless, I'm thinking the solve, which I will submit if agreed upon, is that for a `runtime` type of `provided` it should be searching for `bootstrap`  no extension at all.  I don't even know that it needs to set the handler at all.. Maybe it does for Localstack.


event, context, handler=handler, main_file=main_file)
            return result
        return execute
    raise ClientError(error_response(
        'Unable to extract Java Lambda handler - file is not a valid zip/jar file', 400, error_type='ValidationError'))
def set_archive_code(code, lambda_name, zip_file_content=None):
    
    lambda_arn = func_arn(lambda_name)
    lambda_details = arn_to_lambda[lambda_arn]
    is_local_mount = code.get('S3Bucket') == BUCKET_MARKER_LOCAL
    if is_local_mount and config.LAMBDA_REMOTE_DOCKER:
        msg = 'Please note that Lambda mounts (bucket name "%s") cannot be used with LAMBDA_REMOTE_DOCKER=1'
        raise Exception(msg % BUCKET_MARKER_LOCAL)
    
    LAMBDA_EXECUTOR.cleanup(lambda_arn)
    if is_local_mount:
        
        
        
        
        return code['S3Key']
    
    zip_file_content = zip_file_content or get_zip_bytes(code)
    
    code_sha_256 = base64.standard_b64encode(hashlib.sha256(zip_file_content).digest())
    lambda_details.get_version('$LATEST')['CodeSize'] = len(zip_file_content)
    lambda_details.get_version('$LATEST')['CodeSha256'] = code_sha_256.decode('utf-8')
    tmp_dir = '%s/zipfile.%s' % (config.TMP_FOLDER, short_uid())
    mkdir(tmp_dir)
    tmp_file = '%s/%s' % (tmp_dir, LAMBDA_ZIP_FILE_NAME)