because of some issues such as having SSR, SSG, and CSR beside each other, I decided to create my own SSR for React js with express js, I'm using redux and saga, and I have several API calls to generate the data before rendering it.
so I had to use several promises in my server-side renderer, such as waiting for redux to finish all APIs, or waiting for styles and scripts, also I'm using react-ssr-prepass and it navigates through all my components (for dispatching actions that are required in SSR).
so I have a lot of thread-blocking stuff in my project.
for handling concurrency I started to use node-cluster, so I'll have several nodes on my server and it will increase the concurrency capacity, but it's not the best solution because, under heavy load, even node clustering won't be able to respond to all of the requests.
so I started to think about worker thread or child process in node js, so I make an instance of my server-side renderer on each request and do everything in the background, so concurrent requests won't wait for eachother to be done.
but the issue is in the child process or worker thread I can't use "import", since it's es6
so I have two questions
first of all, is there any way to use es6 in the child process? (I tried babel-esm-plugin but it's not supporting webpack 5)
second, is there any better idea than using worker thread of child process to increase the concurrency capacity?
so I found the solution for my first challenge, instead of running my renderer directly with the child process, I had to build it first, so I used webpack to make a cjs output of it, then use that output in the child process.
and for increase the performance, even more, I used a combination of SSR and SSG, so in each request I check if a file mapped to the route exists on the server, if it's not, I'm gonna use SSR renderer output to create a file, and serve the response to the user, then for next request since the cached file exists I use that cache file instead of rendering the result again.
finally I set a corn job on the server to clear the cache every 10 minute
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I have a question regarding the examples out there when using Nodejs, Express and Jade for templates.
All the examples show how to build some sort of a user administrative interface where you can add user profiles, delete them and manage them.
Those are considered beginner's guides to NodeJs. My question is around the fact that if I have have 10 users concurrently accessing the same interface and doing the same operations, surely NodeJs will block the requests for the other users as they are running on the same port.
So let's say I am pulling out a list of users which may be something like 10000. Yes I can do paging, but that is not the point. While I am getting the list from the server another 4 users want to access the application. They have to wait for my process to end. That is my question - how can one avoid that using NodeJS & Express?
I am on this issue for a couple of months! I currently have something in place that does the following:
Run the main processing of stuff on a port
Run a Socket.io process on a different port
Use a sticky session
The idea is that I do a request (like getting a list of items), and immediately respond with some request reference but without the requested items, thus releasing the port.
In the background "asynchronously" I then do the process of getting the items. Upon which when completed, I do an http request from one node to the socket node port node SENDING the items through.
When that is done I then perform a socket.io emit WITH the data and the initial request reference so that the correct user gets the message.
On the client side I have an event listening for the socket which then completes the ajax request by populating the list.
I have SOME success in doing this! It actually works to a degree! I have an issue online which complicates matters due to ip addresses, and socket.io playing funny.
I also have multiple workers using clustering. I use it in the following manner:
I create a master worker
I spawn workers
I take any connection request and pass it to the relevant worker.
I do that for the main node request as well as for the socket requests. Like I said I use 2 ports!
As you can see I have had a lot of work done on this and I am not getting a proper solution!
My question is this - have I gone all around the world 10 times only to have missed something simple? This sounds way to complicated to achieve a non-blocking nodejs only website.
I asked myself - surely all these tutorials would have not missed on something as important as this! But they did!
I have researched, read, and tested a lot of code - this is my very first time I ask anything on stackoverflow!
Thank you for any assistance.
P.S. One example of the same approach is this: I request a report using jasper, I pass parameters, and with the "delayed ajax response" approach as described above I simply release the port, and in the background a very intensive report is being generated (and this can be very intensive process as a lot of calculations are being performed)..! I really don't see a better approach - any help will be super appreciated!
Thank you for taking the time to read!
I'm sorry to say it, but yes, you have been going around the world 10 times only to have been missing something simple.
It's obvious that your previous knowledge/experience with webservers are from a blocking point of view, and if this was the case, your concerns had been valid.
Node.js is a framework focused around using a single thread to execute code, which means if it does any blocking operations, no one else would be able to get anything done.
There are some operations that can do this in node, like reading/writing to disk. However, most node operations will be asynchronous.
I believe you are familiar with the term, so I won't go into details. What asynchronous operations allows node to do, is to keep this single thread idle as much as possible. By idle I mean open for other work. If your code is fully asynchronous, then handling 4 concurrent users (or even 400) shouldn't be a problem, even for a single thread.
Now, in regards to your initial problem of ports: Once a request is received on a given port, node.js execute whatever code you have written for it, until it encounters an asynchronous operation as soon as that happens, it is available to to pick up more requests on the same port.
The second problem you inquire about, is the database operation. In this case, node-js would send the query to the database (which takes no time at all) and the database does that actual execution of the query. In the meantime, node is free to do whatever it wants, until the database is finished, and lets node know there is a result to fetch.
You can recognize async operations by their structure: my_function(..., ..., callback). Function that uses a callback function, is in most cases asynch.
So bottom line: Don't worry about the problems around blocking IO, as you will hardly encounter any in node. Use a single port if you want (By creating multiple child processes, you can even have multiple node instances on the same port).
Hope this explains it good enough. If you have any further questions, let me know :)
We have a C# Web API server and a Node Express server. We make hundreds of requests from the C# server to a route on the Node server. The route on the Node server does intensive work and often doesn't return for 6-8 seconds.
Making hundreds of these requests simultaneously seems to cause the Node server to fail. Errors in the Node server output include either socket hang up or ECONNRESET. The error from the C# side says
No connection could be made because the target machine actively refused it.
This error occurs after processing an unpredictable number of the requests, which leads me to think it is simply overloading the server. Using a Thread.Sleep(500) on the C# side allows us to get through more requests, and fiddling with the wait there leads to more or less success, but thread sleeping is rarely if ever the right answer, and I think this case is no exception.
Are we simply putting too much stress on the Node server? Can this only be solved with Load Balancing or some form of clustering? If there is an another alternative, what might it look like?
One path I'm starting to explore is the node-toobusy module. If I return a 503 though, what should be the process in the following code? Should I Thread.Sleep and then re-submit the request?
It sounds like your node.js server is getting overloaded.
The route on the Node server does intensive work and often doesn't return for 6-8 seconds.
This is a bad smell - if your node process is doing intense computation, it will halt the event loop until that computation is completed, and won't be able to handle any other requests. You should probably have it doing that computation in a worker process, which will run on another cpu core if available. cluster is the node builtin module that lets you do that, so I'll point you there.
One path I'm starting to explore is the node-toobusy module. If I return a 503 though, what should be the process in the following code? Should I Thread.Sleep and then re-submit the request?
That depends on your application and your expected load. You may want to refresh once or twice if it's likely that things will cool down enough during that time, but for your API you probably just want to return a 503 in C# too - better to let the client know the server's too busy and let them make their own decision then to keep refreshing on its behalf.
I have a node server, which needs to:
Serve the web pages
Keep querying an external REST API and save data to database and send data to clients for certain updates from REST API.
Task 1 is just a normal node tasks. But I don't know how to implement the task 2. This task won't expose any interface to outside. It's more like a background task.
Can anybody suggest? Thanks.
To make a second node.js app that runs at the same time as your first one, you can just create another node.js app and then run it from your first one using child_process.spawn(). It can regularly query the external REST API and update the database as needed.
The part about "Send data to clients for certain updates from REST API" is not so clear what you're trying to do.
If you're using socket.io to send data to connected browsers, then the browsers have to be connected to your web server which I presume is your first node.js process. To have the second node.js process cause data to be sent through the socket.io connections in the first node.js process, you need some interprocess way to communicate. You can use stdout and stdin via child_process.spawn(), you can use some feature in your database or any of several other IPC methods.
Because querying a REST API and updating a database are both asynchronous operations, they don't take much of the CPU of a node.js process. As such, you don't really have to do these in another node.js process. You could just have a setInterval() in your main node.js process, query the API every once in a while, update the database when results are received and then you can directly access the socket.io connections to send data to clients without having to use a separate process and some sort of IPC mechanism.
Task 1:
Express is good way to accomplish this task.
You can explore:
http://expressjs.com/
Task 2:
If you are done with Expressjs. Then you can write your logic with in Express Framework.
This task then can be done with node module forever. Its a simple tool that runs your background scripts forever. You can use forever to run scripts continuously (whether it is written in node.js or not)
Have a look:
https://github.com/foreverjs/forever
I am still pretty new to NodeJS and want to know if I am looking at this in the wrong way.
Background:
I am making an app that runs once a week, generates a report, and then emails that out to a list of recipients. My initial reason for using Node was because I have an existing front end already built using angular and I wanted to be able to reuse code in order to simplify maintenance. My main idea was to have 4+ individual node apps running in parallel on our server.
The first app would use node-cron in order to run every Sunday. This would check the database for all scheduled tasks and retrieve the stored parameters for the reports it is running.
The next app is a simple queue that would store the scheduled tasks and pass them to the worker tasks.
The actual pdf generation would be somewhat CPU intensive, so this would be a cluster of n apps that would retrieve and run individual reports from the queue.
When done making the pdf, they would pass to a final email app that would send the file out.
My main concerns are communication between apps. At the moment I am setting up the 3 lower levels (ie. all but the scheduler) on separate ports with express, and opening http requests to them when needed. Is there a better way to handle this? Would the basic 'net' work better than the 'http' package? Is Express even necessary for something like this, or would I be better off running everything as a basic http/net server? So far the only real use I've made of Express is to specifically listen to a path for put requests and to parse the incoming json. I was led to asking here because in tracking logs so far I see every so often the http request is reset, which doesn't appear to affect the data received on the child process, but I still like to avoid errors in my coding.
I think that his kind of decoupling could leverage some sort of stateful priority queue with features like retry on failure, clustering, ...
I've used Kue.js in the past with great sucess, it's redis backed and has nice documentation and interface http://automattic.github.io/kue/
I'm using NodeJS to run a socket server (using socket.io). When a client connects, I want am opening and running a module which does a bunch of stuff. Even though I am careful to try and catch as much as possible, when this module throws an error, it obviously takes down the entire socket server with it.
Is there a way I can separate the two so if the connected clients module script fails, it doesn't necessarily take down the entire server?
I'm assuming this is what child process is for, but the documentation doesn't mention starting other node instances.
I'd obviously need to kill the process if the client disconnected too.
I'm assuming these modules you're talking about are JS code. If so, you might want to try the vm module. This lets you run code in a separate context, and also gives you the ability to do a try / catch around execution of the specific code.
You can run node as a separate process and watch the data go by using spawn, then watch the stderr/stdout/exit events to track any progress. Then kill can be used to kill the process if the client disconnects. You're going to have to map clients and spawned processes though so their disconnect event will trigger the process close properly.
Finally the uncaughtException event can be used as a "catch-all" for any missed exceptions, making it so that the server doesn't get completely killed (signals are a bit of an exception of course).
As the other poster noted, you could leverage the 'vm' module, but as you might be able to tell from the rest of the response, doing so adds significant complexity.
Also, from the 'vm' doc:
Note that running untrusted code is a tricky business requiring great care.
To prevent accidental global variable leakage, vm.runInNewContext is quite
useful, but safely running untrusted code requires a separate process.
While I'm sure you could run a new nodejs instance in a child process, the best practice here is to understand where your application can and will fail, and then program defensively to handle all possible error conditions.
If some part of your code "take(s) down the entire ... server", then you really to understand why this occurred and solve that problem rather than rely on another process to shield you from the work required to design and build a production-quality service.