I am very new to Node.js and express. I am currently learning it by building my own services.
I recently read about clusters. I understood what clusters do. What I am not able to understand is how to make use of clusters in a production application.
One way I can think of is to use the Master process to just sit in front and route the incoming request to the next available child process in a round robin fashion. I am not sure if this is how it is designed to be used. I would like to know how should clusters be used in a typical web application.
Thanks.
The node.js cluster modules is used with node.js any time you want to spread out the request processing across multiple node.js processes. This is most often used when you wish to increase your ability to handle more requests/second and you have multiple CPU cores in your server. By default, a single instance of node.js will not fully utilize multiple cores because the core Javascript you run in your server is single threaded (uses one core). Node.js itself does use threads for some things internally, but that's still unlikely to fully utilize a mult-core system. Setting up a clustered node.js process for each CPU core will allow you to better maximize the available compute resources.
Clustering also provides you with some additional fault tolerance. If one cluster process goes down, you can still have other live clusters serving requests while the disabled cluster restarts.
The cluster module for node.js has a couple different scheduling algorithms - the round robin you mention is one. You can read more about that here: Cluster Round-Robin Load Balancing.
Because each cluster is a separate process, there is no automatic shared data among the different cluster processes. As such, clustering is simplest to implement either where there is no shared data or where the shared data is already in a place that it can be accessed by multiple processes (such as in a database).
Keep in mind that a single node.js process (if written to properly use async I/O and not heavily compute bound) can server many requests itself at once. Clustering is when you want to expand scalability beyond what one instance can deliver.
I have created a poc on cluster in nodejs and added some details in the below blogs. Once go through it. It may provide some clearance.
https://jksnu.blogspot.com/2022/02/cluster-in-node-js-application.html
https://jksnu.blogspot.com/2022/02/cluster-management-in-node-js.html
Related
I built an app on node.js using Docker and I'm not sure how to scale it on a Kubernetes cluster so that I take the most out of my cluster hardware.
From a performance perspective which of the following is better:
clusterize my node app and run as many containers as needed
or
just run as many containers as needed without clustering ?
When I say clustering I mean this https://nodejs.org/api/cluster.html
My app is a simple CRUD Api backed by mongoDB. We estimate that it will have 1000 concurrent users. Our cluster has 3 nodes.
The NodeJS cluster mechanism is useful to allow NodeJS to more effectively use greater than a single core, so depending on your code it may benefit you, but it's highly dependent on your code and the various dependencies and how well they work (or not) with clustering.
As a general practice, if you can break your containers down into nicely parallelized efforts that can be run as pods within kubernetes, then I'd recommend the following as a process to see what works for you:
set up a single pod with your code in it, and run a load test against it. Use the data that Kubernetes has from cAdvisor to characterize how much resources (cpu & memory) your pod likes to have.
set a resource limit for cpu and memory based on what you see above.
run a load test to validate what your single pod handles in terms of scale
And from there, you have a baseline where you can use Kubernetes to scale this horizontally to validate the 1000 user concurrent baseline you want to achieve.
There's a good talk on this process from the 2017 Kubecon called Load Testing Kubernetes: How to optimize your cluster resource allocation in production
Once you have a baseline, you can run a prototype out leveraging the clustering in your code, and then compare against the non-clustered version. If you do this, I'd double-check that any limits you set are > 1 core for CPU, or you'll be self-limiting outside of the NodeJS runtime to get access to multiple cores, which would defeat the purpose of using clustering.
Depending on what you're doing in your code, there may be significant re-work needed to enable clustering, as it wants to leverage its own worker concept, and it's not clear what frameworks you're using and if they'll fit reasonably into that structure.
Ok guys, is it useful to generate more than one websocket instance on a Node.js server? I mean possibly you also create subworkers..
I know, it depends on your hardware and the network cards maximum. But can you reach this maximium with only one task or can you get more performance with several parallel processes?
It depends on the CPU count in your server. Parallel processes (the cluster module) aren't a silver bullet for performance - on a 1 CPU system they might even decrease it just due to overhead. But if you have more than one CPU, a NodeJS process CANNOT use that extra horsepower. The cluster module solves this. Used properly you can use all the available CPU power on the system.
Note that this has nothing to do with WebSockets themselves. This is a core NodeJS architectural constraint. But WebSockets are a great use-case where clustering is advantageous...
"Node.js is limited to a single thread". how the nodeJS will react when we are deploying in Multi-Core systems? will it boost the performance?
The JavaScript running in the Node.js V8 engine is single-threaded, but the underlying libuv multi-platform support library is multi-threaded and those threads will be distributed across the CPU cores by the operating system according to it's scheduling algorithm, so with your JavaScript application running asynchronously (and single-threaded) at the top level, you still benefit from multi-core under the covers.
As others have mentioned, the Node.js Cluster module is an excellent way to exploit multi-core for concurrency at the application (JavaScript V8) level, and since Express is cluster aware, you can have multiple worker processes executing concurrent server logic, without needing a unique listening port for each process. Impressive.
As others have mentioned, you will need Redis or equivalent to share data among the cluster worker processes. You will also want a logging facility that is cluster aware, so the cluster master and all worker processes can log to a single shared log file. The Node log4node module is a good choice here, and it works with logrotate.
Typical web examples show using the runtime detected number of cores as the number of cluster worker processes to fork, but I prefer to make that a configuration option in a config.yaml file so I can tune the number of worker processes running the main JavaScript application as needed.
Nodejs runs in one thread, but you can start multiple nodejs processes.
If you are, for example, building web server you can route every request to one of nodejs processes.
Edit: As hereandnow78 and vkurchatkin suggested, maybe the best way to use power of multi core system would be to use nodejs cluster module
cluster module is the solution.
But u need to know that, node.js cluster is, it invokes child process. It means each process cannot share the data.
To share data, u need to use Redis or other IMDG to share the data across the cluster nodes.
I have an application that runs long-executing processes. To make it faster, I do simple sharding of data and want to run them in parallel, simply by .fork() 2 instances of same application.
I'm having 2 Cores machine there and want to make sure that 2 Cores are utilized and first instance is running on first core, second on second core.
I know about cluster module, but it seems not relevant in this case, since I don't need HTTP services running and load-balancing between them. Just workers (mean, they dont need to communicate with each other, send messages or whatever - they just do HTTP requests and store data to database).
Is there possible at all to control which CPU core would node.js process take? How to monitor that on Mac/Linux?
Cluster module is exactly what you need : http://nodejs.org/api/cluster.html
You want this, which is a specific part of the cluster API:
cluster.setupMaster([settings])
https://nodejs.org/api/cluster.html#cluster_cluster_setupmaster_settings
I also wrote a module to do this, and there are several out there:
https://www.npmjs.com/package/poolio
my module works well, but the API is not that straightforward, so I would recommend using the core module
Creating a node.js application is simple enough.
var app = require('express')();
app.get('/',function(req,res){
res.send("Hello world!");
});
But suppose people became obsessed with your Hello World! application and exhausted your resources. How could this example be scaled up on practice? I don't understand it, because yes, you could open several node.js instance in different computers - but when someone access http://your_site.com/ it aims directly that specific machine, that specific port, that specific node process. So how?
There are many many ways to deal with this, but it boils down to 2 things:
being able to use more cores per server
being able to scale beyond more than one server.
node-cluster
For the first option, you can user node-cluster or the same solution as for the seconde option. node-cluster (http://nodejs.org/api/cluster.html) essentially is a built in way to fork the node process into one master and multiple workers. Typically, you'd want 1 master and n-1 to n workers (n being your number of available cores).
load balancers
The second option is to use a load balancer that distributes the requests amongst multiple workers (on the same server, or across servers).
Here you have multiple options as well. Here are a few:
a node based option: Load balancing with node.js using http-proxy
nginx: Node.js + Nginx - What now? (using more than one upstream server)
apache: (no clearly helpful link I could use, but a valid option)
One more thing, once you start having multiple processes serving requests, you can no longer use memory to store state, you need an additional service to store shared states, Redis (http://redis.io) is a popular choice, but by no means the only one.
If you use services such as cloudfoundry, heroku, and others, they set it up for you so you only have to worry about your app's logic (and using a service to deal with shared state)
I've been working with node for quite some time but recently got the opportunity to try scaling my node apps and have been researching on the same topic for some time now and have come across following pre-requisites for scaling:
My app needs to be available on a distributed system each running multiple instances of node
Each system should have a load balancer that helps distribute traffic across the node instances.
There should be a master load balancer that should distribute traffic across the node instances on distributed systems.
The master balancer should always be running OR should have a dependable restart mechanism to keep the app stable.
For the above requisites I've come across the following:
Use modules like cluster to start multiple instances of node in a system.
Use nginx always. It's one of the most simplest mechanism for creating a load balancer i've came across so far
Use HAProxy to act as a master load balancer. A few pointers on how to use it and keep it forever running.
Useful resources:
Horizontal scaling node.js and websockets.
Using cluster to take advantages of multiple cores.
I'll keep updating this answer as I progress.
The basic way to use multiple machines is to put them behind a load balancer, and point all your traffic to the load balancer. That way, someone going to http://my_domain.com, and it will point at the load balancer machine. The sole purpose (for this example anyways; in theory more could be done) of the load balancer is to delegate the traffic to a given machine running your application. This means that you can have x number of machines running your application, however an external machine (in this case a browser) can go to the load balancer address and get to one of them. The client doesn't (and doesn't have to) know what machine is actually handling its request. If you are using AWS, it's pretty easy to set up and manage this. Note that Pascal's answer has more detail about your options here.
With Node specifically, you may want to look at the Node Cluster module. I don't really have alot of experience with this module, however it should allow you to spawn multiple process of your application on one machine all sharing the same port. Also node that it's still experimental and I'm not sure how reliably it will be.
I'd recommend to take a look to http://senecajs.org, a microservices toolkit for Node.js. That is a good start point for beginners and to start thinking in "services" instead of monolitic applications.
Having said that, building distributed applcations is hard, take time to learn, take LOT of time to master it, and usually you will face a lot trade-off between performance, reliability, manteinance, etc.