Running multiple Node apps on Node cluster

Question

We need to deploy multiple Node/Express apps on a set of servers (behind load balancer). These apps are fully independent of each other in terms of functionality. I'll first explain how I am thinking of doing this and then I am looking for input in terms of best practices, if there are any red flags in my design etc.

Here is the setup I am thinking about:

Frontend server behind load balancer will have node-http-proxy running and it'll accept incoming requests on port 80. This reverse proxy will route the requests to appropriate node apps that are running on different ports on this server. for ex:

var http = require('http'),
    httpProxy = require('http-proxy');

var options = {
  router: {
    'myapphost.com/MyFirstApp': 'myapphost.com:3000',
    'myapphost.com/MySecondApp': 'myapphost.com:3001'
  }
}

// ...and then pass them in when you create your proxy.
var proxyServer = httpProxy.createServer(options).listen(80);

Each of the node app will be running on node cluster using something like Cluster2 to take advantage of multi-core systems.

My questions:

Is this right design and strategy?
Some of our applications need to be stateful. What is the best way to do the state management in this kind of a setup? Using external session storage such as Redis is the right approach? Or pinning a session to a given frontend machine and using in-memory session storage?

UPDATE:

Since I posted this question, after talking to couple of people, there is one more approach that has come up--

I can use Nginx as a reverse proxy and load balancer in front of my frontend machines. Each frontend machine will serve only one app. There can be one more back up machine for that app. (depending upon requirement). So if I have three apps, I'll have three separate machines each one serving different app. All the requests will be received by Nginx on port 80, Nginx reverse proxy will route the request to the right frontend machine. Each machine will have Node cluster to take advantage of multi-core system. Advantage of this approach is-- deployment becomes lot easier for each app. Also, we can scale each app separately.

Please share your thoughts on this approach as well.

score 0 · Answer 1 · answered Oct 15 '13 at 09:49

This is a right approach, as well you mentioned redis, or you could use any other session storages like connect-mongo or any other session storage.
If you are using Load Balancer, I guess you have multiple instances of same servers? If this is the case, then you need to analyze session performance and how much it will be used, and then decide if you need to shard session storage/database, or one single machine that every balanced instance will be talking to.

You already think the right way, why wont you try and hack some of it, and see if it fits your needs?

As well you need to think about static media, possibly to store it separately (S3 + CloudFront?).
As well as how you are going to deliver updates to instances and restart them while still keeping application logic consistency.

This structure as well enables possibilities for AB testing (you can load balance to specific instances with "testing version" of application. While majority will be balanced across main instances.

It all depends on your scale as well, and sometimes you really don't need that much initially, just be ready to improve and scale in the future.

Running multiple Node apps on Node cluster

1 Answers1