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We have several Kinesis streams set up with event notifications that trigger lambdas.  When the LAMBDA_EXECUTOR is set to 'docker' and we send a large number or records to Kinesis, multiple Lambdas will execute, but currently they are failing to create with error:

```
Exception: Lambda process returned error status code: 1. Output:
time="2019-09-18T17:28:11Z" level=error msg="error getting events from daemon: net/http: request canceled" 
Error response from daemon: driver failed programming external connectivity on endpoint busy_sanderson (a78e45a41d0ce5b0d8bab6ff54344fc34fe2b4969f55bf568e753121abc8759e): Bind for 0.0.0.0:38763 failed: port is already allocated
```

I believe this is due to the new debug_java_port introduced with this PR https://github.com/localstack/localstack/pull/1523

With this change, you are setting the port in the constructor by using a method known to have a race condition (https://github.com/localstack/localstack/blob/master/localstack/utils/common.py#L354)
(https://gist.github.com/gabrielfalcao/20e567e188f588b65ba2)

This should be changed to ensure unique ports are being issued across all lambdas


return result, log_output
    def execute_java_lambda(self, event, context, handler, main_file):
        event_file = EVENT_FILE_PATTERN.replace('*', short_uid())
        save_file(event_file, json.dumps(event))
        TMP_FILES.append(event_file)
        class_name = handler.split('::')[0]
        classpath = '%s:%s' % (LAMBDA_EXECUTOR_JAR, main_file)
        cmd = 'java -cp %s %s %s %s' % (classpath, LAMBDA_EXECUTOR_CLASS, class_name, event_file)
        result, log_output = self.run_lambda_executor(cmd)
        LOG.debug('Lambda result / log output:\n%s\n> %s' % (
            result.strip(), log_output.strip().replace('\n', '\n> ')))
        return result, log_output
class Util:
    @staticmethod
    def get_java_opts(port):
        opts = config.LAMBDA_JAVA_OPTS
        if opts.find('_debug_port_'):
            java_opts = opts.replace('_debug_port_', ('%s' % port))
            return java_opts
        return opts
EXECUTOR_LOCAL = LambdaExecutorLocal()
EXECUTOR_CONTAINERS_SEPARATE = LambdaExecutorSeparateContainers()
EXECUTOR_CONTAINERS_REUSE = LambdaExecutorReuseContainers()
DEFAULT_EXECUTOR = EXECUTOR_LOCAL
AVAILABLE_EXECUTORS = {
    'local': EXECUTOR_LOCAL,
    'docker': EXECUTOR_CONTAINERS_SEPARATE,
    'docker-reuse': EXECUTOR_CONTAINERS_REUSE
}