I've been doing a lot of research lately and it appears to me that going stateless serverside brings benefits to both performance & scalability.
I am although trying to figure out how to achieve session-less-ness on Node.JS. It seems to me that basically all I have to do is assign a token to a logged in user, so I would have something like this in my DB:
{ user:'foo#example.com', pass:'123456', token:'long_id_here' }
so that the token can be send with every HTTP request like this:
/set/:key/:val/:token
to be checked against aforementioned DB object. Is this what it is actually meant to be a session-less web service?
If this is the right way, then I do not understand things like token expiry, and other security issues. I would like to be pointed out to NPM package of some sort?
On a side note, is it best for a token, to use a hash of the user+password, or to assign a different one at every login?
The reason to go sessionless is that most default session implementations use an in-memory store. That means that the session information is stored in memory local to that instance. Most websites these days are scaling out as traffic increases. This means they add more servers and balance the load between the servers. The problem with in-memory session stores is your user can log into Server 1, but if their next request is routed to Server 2, they don't have a session created yet and will appear to be logged off.
You don't necessarily need to go sessionless to scale out with node or any other server side language. You just need to use a session that isn't in local memory that would be accessible to all nodes. If you're using something like Express or Connect, you can easily use a session implementation like connect-redis which will enable you to have a fast session store which is accessible to all of your node instances so it doesn't matter which one is hit.
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I have an app that receives data from several sources in realtime using logins and passwords. After data is recieved it's stored in memory store and replaced after new data is available. Also I use sessions with mongo-db to auth user requests. Problem is I can't scale this app using pm2, since I can use only one connection to my datasource for one login/password pair.
Is there a way to use different login/password for each cluster or get cluster ID inside app?
Are memory values/sessions shared between clusters or is it separated? Thank you.
So if I understood this question, you have a node.js app, that connects to a 3rd party using HTTP or another protocol, and since you only have a single credential, you cannot connect to said 3rd party using more than one instance. To answer your question, yes it is possibly to set up your clusters to use a unique use/pw combination, the tricky part would be how to assign these credentials to each cluster (assuming you don't want to hard code it). You'd have to do this assignment when the servers start up, and perhaps use a a data store to hold these credentials and introduce some sort of locking mechanism for each credential (so that each credential is unique to a particular instance).
If I was in your shoes, however, what I would do is create a new server, whose sole job would be to get this "realtime data", and store it somewhere available to the cluster, such as redis or some persistent store. The server would then be a standalone server, just getting this data. You can also attach a RESTful API to it, so that if your other servers need to communicate with it, they can do so via HTTP, or a message queue (again, Redis would work fine there as well.
'Realtime' is vague; are you using WebSockets? If HTTP requests are being made often enough, also could be considered 'realtime'.
Possibly your problem is like something we encountered scaling SocketStream (websockets) apps, where the persistent connection requires same requests routed to the same process. (there are other network topologies / architectures which don't require this but that's another topic)
You'll need to use fork mode 1 process only and a solution to make sessions sticky e.g.:
https://www.npmjs.com/package/sticky-session
I have some example code but need to find it (over a year since deployed it)
Basically you wind up just using pm2 for 'always-on' feature; sticky-session module handles the node clusterisation stuff.
I may post example later.
I'm trying to create a Flash app with some real time functionality, and would like to use Redis' pubsub functionality which is a perfect fit for what I need.
I know that connecting to a data store directly from client is almost always bad. What are the security implications of this (since I'm not an expert on Redis), and are there ways to work around them? From what I read, there is a possible exploit of doing config sets and changing the rdb file location and be able to arbitrary overwrite files. Is there anything else? (If I don't use that particular redis instance for anything at all, i.e. no data being stored)
I understand the alternative is to write some custom socket server program and have it act as the mediating layer for connecting to redis and issuing commands -- that's the work I'd like to avoid having to write, if possible.
** Edit **
Just learned about the rename-command configuration to disable commands. If I disable every single command on the redis instance and leave only SUBSCRIBE and PUBLISH open, would this be good enough to run on production?
I think it would be a bad idea to connect directly your client to Redis. Redis offers an authentication system for a unique user only. It expects this user to be your server app.
From my point of view, directly exposing Redis is always a bad idea. It would allow anybody to access all of your data. This is confirmed by the Redis doc.
So you won't avoid adding or developing the server side of your app.
I am building a really simple web application with Node.js. The purpose of this application is to allow a user to edit settings of some running computations from a browser. I would like to restrict the application to allow only one user at a time, so to avoid any conflicts. If another user connects to the application while some user is already there, the second one should be notified, that the application is in use by another user.
What is a preffered way to achieve this with Node.js?
I would recommend you build a simple session object ("model") that manages the connected users and only allows one connected session at a time. Perhaps sessions could timeout after 90 seconds of inactivity.
Here's a quick sessions tutorial which shows you how to use a raw session (req.session), a redis backend, or a mongodb backend. A basic express middleware could be used to manage the sessions and set a limit of 1.
If you want something more advanced, maybe look into Passport.
I am running a Node.js server which is now getting more load and I need to start getting this running on multiple cores, as Node.js is single threaded and can only run on one.
This is a simple solution given the Node.js Cluster module and tons of NPM packages for this very thing.
I have a problem in that I need browser sessions to retain the same Node.js worker after the first request. This is because I store authentication data, etc. in a single node worker process and do not want to open the can of worms of messaging between worker processes, etc. etc.
My browsers store a session id cookie once authenticated, and I want a system to re-route requests to their correct worker based on their session cookie.
Nginx looks promising, but I know nothing about it, and while I will put the work into it, I would like to know before I spend hours diving into it, if it is capable of routing to Node.js worker processes based on arbitrary data from the request header, such as a session cookie.
Is this doable? If I know it is, I'll get down and dirty figuring out Nginx, ground up.
I assume you are storing your sessions in nodejs memory. You might want to store your sessions in redis instead. This way it is persisted outside of a single server, and can be accessed from multiple processes.
In addition to redis, you might also want to look into Amazon Elastic Beanstalk for managing your load-balancing. You can setup an nginx proxy to route your requests to multiple servers based on their load.
This link might be able to get you started http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/create_deploy_nodejs_express_elasticache.html
I am about to start a new XPage project which will be used world-wide. I am a bit concerned because they are worried about performance and are therefore thinking about using this application in with a load balancer or a in a cluster. I have been looking around and I have seen that there can be issues with scoped variables (for example of the user starts the session on one server and is then sent to another, certain scoped variables go missing). I have also seen this wonderful article which focuses on performance, but does not really mention anything about a clustered environment.
Just a bit of extra info: concurrent users should not be higher than 600, but may grow over time, there are about 3000 users total. The XPage application will be a portal for a two data sources (an active database and its archive).
My question is this: as a developer, what must I pay very close attention to when developing an application that may run behind a load balancer or in a clustered environment?
Thanks for your time!
This isn't really an answer...but I can't fit this in a comment.
We faced a very similar problem.
We have an xpage SPA (Single Page Application) application that has been in production for 2-3 years, with variable user load up to 300-400 concurrent users who login for 8 hr sessions, we have 4 clustered Domino servers, 1 being a "workhorse" running all scheduled jobs, and 3 dedicated HTTP servers.
We use SSO in Domino and the 3 HTTP servers participate, so a user only has to authenticate once and can access all HTTP servers. We use a reverse proxy, so all users go to www.ourapp.com but get redirected to servera.ourapp.com, serverb.ourapp.com, etc., once they get directed to a server, the rev proxy issues a cookie to the client. This provides a "sticky" session to whichever server they have been directed to, and rev proxy will only move them to a different server if the server they are on becomes unavailable.
We use "user" managed session beans to store config for each user, so if the user moves server, if the user's bean does not exist, it will be created. But they key point is: because of sticky session, the user will only move if we bring a server down or the server was to fail. Since our app is a SPA, a lot of the user "config" is stored client side, so if they get booted to a different server (to the user, they are still pointed to www.ourapp.com) nothing really changes.
This has worked really well for us so far.
The app is also accessed by an "offline" external app, it points to the rev proxy (www.ourapp.com), but we did initially run into problems because this app was not passing back the Rev Proxy "sticky" cookie token, so 1 device was sending a request to proxy which got routed to server A, then 1 sec later to server B, then A..B..C, all sorts of headaches...since the cluster can be a few seconds out of sync, if sending requests to same doc...conflicts. As soon as we got the external app to pass back rev proxy token for each session, problem solved.
The one bit of your question I don't quite understand is: "...The XPage application will be a portal for a single database (no replicas) and an archive database (no replicas). " Does that mean the portal will be clustered, but the DB users are connecting to will not be clustered?
We haven't really coded any differently than if app was on 1 server, since the user's session is "stuck" to one server. We did need persistent document locking across all the servers. We initially used the native document locking, but $writers does not cluster, so we had to implement our own...we set a field on doc so that "lock" clustered (we also had to then implement s single lock store...sigh, can talk about that another time). Because of requirements, we have to maintain close to 1 million docs in 3 of the app databases, we generate huge amounts of audit data, but we push that out to SQL.
So I'd say this is more of an admin headache (I'm also the admin for this project, so in our case I can confirm this!) than a designer headache.
I'd also be interested to hear what anyone else has to say on this subject.