CPU utilization of Node.js on Amazon EC2

Question

Seeing as how node is single threaded, If I have node server running on an amazon EC2 instance with 4 EC2 Compute units will it run any faster / handle more load than if I have 2 EC2 Compute units?

Does CPU utilization on amazon require a program to be multithreaded to fully use all resources?

Answer 1

To fully utilize compute resources of N cores, you need at least N threads ready to do useful work. This has nothing to do with EC2; it's just the way computers work. I assume from your question that you are choosing between the m1.medium and m1.large instance types, which have 1 and 2 dedicated cores, respectively (the m1.small is half of a shared core, and the m1.xlarge is the full dedicated 4-core box). Thus, you need at least 2 processes doing useful work in order to utilize the larger box (unless you just want access to more memory / io).

Each Node.js process is single threaded by design. This lets it provide a clean programming paradigm free of locking semantics. This is very much by design.

For a Node.js app to utilize multiple cores, it must spawn multiple processes. These processes would then use some form of messaging (pipes, sockets, etc) to communicate -- versus "shared memory" where code can directly mutate memory locations visible to multiple processes, something that would require locking semantics.

In practice, this is dirt simple easy to set up. Back in Node.JS v0.6.X the "cluster" module was integrated into the standard distribution, making it easy to set up multiple node workers that can listen on a single port. Note that this "cluster" module is NOT the same as the learnboost "cluster" module which has a different API and owns the "cluster" name in the NPMjs registry.

http://nodejs.org/docs/latest/api/cluster.html

if (cluster.isMaster) {   // Fork workers.   for (var i = 0; i &lt numCPUs; i++) {     cluster.fork();   } } else {   http.Server(function(req, res) { ... }).listen(8000); } 

Answer 2

The short answer to your question is that adding more cores in order to improve your node performance will not work, if all you do is write "standard" single threaded javascript (you will be bound by a single CPU).

The reason is that node.js uses an event loop for processing, so if all you are doing is starting up a single node.js process without anything else, it will not be multi-threaded and thus not use more than one CPU (core).

However, you can use the node.js cluster API to fork the node process so you can take advantage of multiple CPUs (cores): https://nodejs.org/docs/latest/api/cluster.html. If you write your code that way, then having more compute units will help you.

There is one caveat, in that EC2 compute units are detailed per instance. For some instances you can get more "compute units" per virtual core. So if you pick an instance that has 2 compute units per virtual core versus one that has one per core, you will be able to execute node on a CPU that has more compute units. However, it looks like after 2 compute units the computing power is split per core which means you won't get any benefit from the multiple cores.