Sunday, April 16, 2017

Ruminating on the single-threaded model of NodeJS and Node-RED

Many developers and architects have asked me questions on the single-threaded nature of NodeJS and whether we can use it effectively on multi-core machines. Since Node-RED is based on NodeJS, whatever is valid for NodeJS is also valid for Node-RED.

NodeJS has a single thread per process model. When you start NodeJS, it would start a single process with one thread in it. Due to it's non-blocking IO paradigm, it can easily handle multiple client requests concurrently, as there is no thread that is blocking for any IO operation.

Now the next question is around the optimal usage of multi-core machines. If you have 8 core or 16 core machines on your cloud and just run one NodeJS process on it, then you are obviously under-utilizing the resources you have paid for. In order to use all the cores effectively, we have the following options in NodeJS:

1) For compute-intensive tasks: NodeJS can fork out child processes for heavy-duty stuff - e.g. if you are processing images or video files, you can fork out child NodeJS processes from the parent process. Communication between parent and child processes can happen over IPC.

2) For scaling REST APIs: You can start multiple NodeJS processes on a single server - e.g. if you have 8 cores, start 8 NodeJS processes. Put a load balancer (e.g. nginx) in front of these processes. You would anyways have some kind of load-balancing setup in your production environment and the same can be leveraged.

3) Cluster support in newer versions on NodeJS: In the latest versions of NodeJS, you have support for Clusters. Cluster enables us to start multiple NodeJS processes that all share the same server port - e.g. 8 NodeJS processes all listening to port 80.  This is the best OOTB option available today in NodeJS.

Hence it is indeed possible to effectively utilize NodeJS on multi-core machines. A good discussion on the same is available on StackOverflow here.

Another interesting question that is often asked is whether Java developers should jump ship and start development in NodeJS because of its speed and simplicity. Also, NodeJS evangelists keep harping about the fact that the single-threaded nature of Node removes the complexity of multi-threading, etc.

Here are my thoughts on this:

1) Today Java has first class support for non-blocking IO, similar to NodeJ. Take a look at the superb open-source  Netty library that powers all the cloud services at Apple.

2) Most of the complexity of multithreading is abstracted away by popular frameworks such as Spring - e.g. Spring Cloud enables developers to write highly scalable and modular distributed applications that are cloud-native without dealing with the complexities of multi-threading.

3) The Servlet 3.0 specification introduced async requests and the Spring REST MVC framework also supports non-blocking REST services as described here.  

Thus today, all the goodies of NodeJS are available on the Java platform. Also plenty of  Java OSS to kick start your development with all the necessary plumbing code.

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