The lambda execution is not suspending and the lambda container has no port exposed when running a java 11 lambda with the latest localstack docker image by docker-compose with the environment variable LAMBDA_JAVA_OPTS=-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=_debug_port_
    
It works fine for java8 runtime executions.

Docker command:

> localstack_1  | 2020-01-26T12:42:04:INFO:localstack.services.awslambda.lambda_executors: Running lambda cmd: CONTAINER_ID="$(docker create -i   -e ENV="$ENV" -e DOCKER_LAMBDA_USE_STDIN="$DOCKER_LAMBDA_USE_STDIN" -e HOSTNAME="$HOSTNAME" -e LOCALSTACK_HOSTNAME="$LOCALSTACK_HOSTNAME" -e AWS_LAMBDA_FUNCTION_TIMEOUT="$AWS_LAMBDA_FUNCTION_TIMEOUT" -e AWS_LAMBDA_FUNCTION_NAME="$AWS_LAMBDA_FUNCTION_NAME" -e AWS_LAMBDA_FUNCTION_VERSION="$AWS_LAMBDA_FUNCTION_VERSION" -e AWS_LAMBDA_FUNCTION_INVOKED_ARN="$AWS_LAMBDA_FUNCTION_INVOKED_ARN"  --rm "lambci/lambda:java11" "com.XXX.XXX.Handler")";docker cp "/tmp/localstack/zipfile.0c90736c/." "$CONTAINER_ID:/var/task"; docker start -ai "$CONTAINER_ID";

I think this is due to the fact that the classpath arguments and java opts are only being set if the rutime is equal to LAMBDA_RUNTIME_JAVA8 (line 211 of ocalstack/localstack/services/awslambda/lambda_executors.py , commit 03c6f4bf250edd18eb818ed65090f508636b0bff)
lambda_handler = generic_handler
    if is_java_lambda(runtime):
        
        
        
        lambda_handler = get_java_handler(zip_file_content, handler_name, tmp_file)
    if not is_local_mount:
        
        if not is_zip_file(zip_file_content):
            raise ClientError(
                'Uploaded Lambda code for runtime ({}) is not in Zip format'.format(runtime))
        
        if not is_java_lambda(runtime) or zip_contains_jar_entries(zip_file_content, 'lib/'):
            unzip(tmp_file, lambda_cwd)
    
    if not is_java_lambda(runtime):
        handler_file = get_handler_file_from_name(handler_name, runtime=runtime)
        handler_function = get_handler_function_from_name(handler_name, runtime=runtime)
        main_file = '%s/%s' % (lambda_cwd, handler_file)
        if not os.path.exists(main_file):
            
            
            
            if not is_local_mount or not use_docker() or config.LAMBDA_REMOTE_DOCKER:
                file_list = run('cd "%s"; du -d 3 .' % lambda_cwd)
                config_debug = ('Config for local mount, docker, remote: "%s", "%s", "%s"' %
                    (is_local_mount, use_docker(), config.LAMBDA_REMOTE_DOCKER))
                LOG.debug('Lambda archive content:\n%s' % file_list)
                raise ClientError(error_response(
                    'Unable to find handler script (%s) in Lambda archive. %s' % (main_file, config_debug),