Graceful shutdown of forked workers in Python and JavaScript running in Docker containers

You might encounter a situation where you want to fork a script during execution. For example if the amount of forks is dependent on user input or another specific situation. I encountered such a situation in which I wanted to put load on a service using multiple concurrent processes. In addition, when running in a docker container, only the process with PID=1 receives a SIGTERM signal. If it has terminated, the worker processes receive a SIGKILL signal and are not allowed a graceful shutdown. In order to do a graceful shutdown of the worker processes, the main process needs to manage them and only exit after the worker processes have terminated gracefully. Why do you want processes to be terminated gracefully? In my case because I store performance data in memory (disk is too slow) and only write the data to disk when the test has completed.

This seems relatively straightforward, but there are some challenges. Also I implemented this in JavaScript running on Node and in Python. Python and JavaScript handle forking differently.

Oracle Mobile Cloud Service (MCS). Implementing custom APIs using JavaScript on Node.js.

Oracle Mobile Cloud Service is a mobile backend as a service. MCS does its magic by providing a lot of features to make implementing mobile services easy such as (among many other) authentication, logging/analytics, lookups and calling other services. There are also features available to make integration with mobile clients easy such as providing an easy way to implement push notifications.

Personally I think one of the most powerful features of MCS is the ability to write custom JavaScript code and use that as an API implementation. This custom code can (among the regular JavaScript features) call MCS connectors and platform services. This provides a lot of flexibility in defining API behavior.

In this blog I will show how you can use this custom Node.js code to create an end to end example. I will use a RAML file to define my interface. Next I will define a connector in MCS to call the OpenWeatherMap API. This API returns (amongst other things) the temperature at a location in Kelvin. I want to define my own custom result message (with the temperature in Celsius) which better matches the requirements of my mobile client. I will use a custom JavaScript implementation to call the connector which calls the OpenWeatherMap API and create a custom response message from the result.

The described example is not suitable for a production implementation and is based on limited experience (and watching some really nice YouTube presentations). It is provided to give an idea on how to get started easily with a simple working example.

Node.js and Oracle NoSQL Database

Oracle NoSQL Database is an interesting option to consider when you want a schemaless, fast, scale-able database which can provide relaxed (eventual) consistency. Oracle provides a Node.js driver for this database. In this blog I'll describe how to install Oracle NoSQL database and how to connect to it from a Node.js application.

The Node.js driver provided by Oracle is currently in preview version 3.3.7. It uses NoSQL client version 12.1.3.3.4 which does not work with 4.x versions of NoSQL database, so I downloaded Oracle NoSQL Database, Enterprise Edition 12cR1 (12.1.3.3.5) from here (the version number was closest to the version number of the client software).

Application Container Cloud: Node.js hosting with enterprise-grade features

Oracle's Application Container Cloud allows you to run Java SE, Node.js and PHP applications (and more is coming) in a Docker container hosted in the Oracle Public Cloud (OPC). Node.js can crash when applications do strange things. You can think of incorrect error handling, blocking calls or strange memory usage. In order to host Node.js in a manageable, stable and robust way in an enterprise application landscape, certain measures need to be taken. Application Container Cloud provides many of those measures and makes hosting Node.js applications easy. In this blog article I'll describe why you would want to use Oracle Application Container Cloud. I'll illustrate this with examples of my experience with the product.

Node.js: My first SOAP service

I created a simple HelloWorld SOAP service running on Node.js. Why did I do that? I wanted to try if Node.js was a viable solution to use as middleware layer in an application landscape. Not all clients can call JSON services. SOAP is still very common. If Node.js is to be considered for such a role, it should be possible to host SOAP services on it. My preliminary conclusion is that it is possible to host SOAP services on Node.js but you should carefully consider how you want to do this.

I tried to create the SOAP service in two distinct ways.

• xml2js. This Node.js module allows transforming XML to JSON and back. The JSON which is created can be used to easily access content with JavaScript. This module is fast and lightweight, but does not provide specific SOAP functionality.
• soap. This Node.js module provides some abstractions and features which make working with SOAP easier. The module is specifically useful when calling SOAP services (when Node.js is the client). When hosting SOAP services, the means to control the specific response to a call are limited (or undocumented)

Using both modules, I encountered some challenges which I will describe and how (and if) I solved them. You can find my sample code here.

Node.js: A simple pattern to increase perceived performance

The asynchronous nature of code running on Node.js provides many interesting options for service orchestration. In this example I will call two translation services (Google and SYSTRAN). I will call both of them quickly after each other (milliseconds). The first answer to be returned, will be the answer returned to the caller. The second answer will be ignored. I've used a minimal set of Node modules for this; http, url, request. Also I wrapped the translation API's to provide a similar interface which allows me to call them with the same request objects. You can download the code here. In the below picture this simple scenario is illustrated. I'm not going to talk about the event loop and the call stack. Watch this presentation for a nice elaboration on those.