Node.js clustering vs multiple Docker containers

Question

From what I understand, Docker containers use multiple threads, and Node.js applications use only a single thread. By running something like pm2, which handles Node.js clustering, I could utilize all cores available to the Docker container.

Would this mean I could have greater utilization of each Docker instance by clustering Node.js processes? If so, wouldn't this be preferred to simply running a single threaded Node.js instance per container?

A concern would be if this has side-effects caused by the possibility of a Docker container scaling up or down the number of CPUs it's running.

score 20 · Accepted Answer · answered Nov 05 '17 at 14:19

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Going straight to the point, it looks like multiple containers perform far better than a single container with cluster support. It's not conclusive, but check this out: Performance and reliability when using multiple Docker containers VS standard Node cluster.

answered Nov 05 '17 at 14:19

stefanobaldo

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Should be noted that the *best option* there explicitly said **multiple containers with cluster support**, i.e. multiple docker containers in each of which there's a Node cluster running (with 4 processes in each). – Milan Velebit Mar 11 '19 at 09:42
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@stefanobaldo the link you provided just points to another question without any evidence, also the question is outdated because there is no mentioning of the dock-compose scale option or kubernetes – MADforFUNandHappy Nov 26 '20 at 11:11

score 1 · Answer 2 · answered Oct 30 '17 at 07:37

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Firstly, you don't essentially need pm2 to run node clusters. node comes with an inbuilt clusters module to take advantage of a multi core machine. Also, scaling down an instance doesn't really have an impact unless you hardcode the number of workers. Refer to the example code in the clusters module to understand how you can spawn workers using clusters.

answered Oct 30 '17 at 07:37

Avinash

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I think the question is about clustering vs multiple docker containers and not app clustering itself - pm2 was just an example :-) – stefanobaldo Nov 05 '17 at 15:45

score 1 · Answer 3 · answered Nov 05 '17 at 18:02

If you are talking about clustering NodeJS inside another docker component I don't think that will give you an extra boost. NodeJS like you said runs in a single thread so either pm2 (I actually use it) or docker will have the same effect in terms of distributing the load.

NodeJS has a concept of web workers to handle how it handles the incoming requests but even a not so fast server will handle hundreds of requests because is a non-blocking architecture.

I recognize I still need to dig into Docker which I want to but I don't have the time but what I would do is to have 1 docker image per server (either virtual or physical) and then have pm2 run several instances of node inside it.

The reason for this is that I want Docker to handle the dependencies for me and I want pm2 to handle the cluster management since it has cool features like restart automatically when the memory reaches a target or to restart an errored node

Perhaps web workers is not the best term but I meant the maxSockets you can configure: http.globalAgent.maxSockets — sebastianf182, Nov 05 '17 at 18:20

Node.js clustering vs multiple Docker containers

3 Answers3