I am using node with vue.js as front-end and Express as back-end. I am furthermore using nodemon. Everything has been working properly until 1 hour ago. Since then, every time I save my code, express crashes with the following error (4000 being my port used):
Error: listen EADDRINUSE: address already in use :::4000
I am required to kill the process (kill -15 PID) and then re-start the server, which re-crashes again upon saving the code. Please note that I haven't launched any new processes or applications since that time.
Edit: I have also noticed that if I run pgrep node, I obtain a list of a dozen processes. Is this normal?
How could this happen?
Related
I want to skip current execution after some blocks of code executed but the server should not stop, It has to be Up and running on the same port using Node js.
I have tried using Process.exit(), Process.kill() and Process.abort() methods as well. It didn't worked as per my expectations. Those are stopping the server.
I need to start the mongoDB server from my NodeJS application. I managed to do this before but for some reason I forgot how. I though I used a cild process but not sure anymore as I can't get anything to work at the moment.
How would I start the mongoDB server (command mongod) from withing my NodeJS app and execute some other code when the server had been started (guessing using a promise...)?
You can use child_process to run mongod from your application, but this may cause the MongoDB server to exit when your app exits. It's generally better to have the DB server running all the time.
https://nodejs.org/api/child_process.html#child_process_child_process_exec_command_options_callback
Why node.js app created as a web server via http.createServer doesn't exit after end as simple console.log() app?
Is it because there is a forever while true {} cycle somewhere in http module?
Deep in the internals of Node.js there is bookkeeping being done. The number of active event listeners is being counted. Events and event-driven programming model are what make Node.js special. Events are also the life blood that keep a Node.js program alive.
A Node.js program will keep running as long as there are active event listeners present. After the last event listener has finished or otherwise terminated the Node.js program will also terminate.
For more details
GO HERE
This is the core of node, that while waiting for new connections, to not exit. Without using loops
There are many other ways, to keep node running, without forever while. For example:
window.setTimeout(function(){},10000000)
In the parent process, I have started the tiny-lr(livereload) server, followed by spawing a child process which looks for changes to the css files. how to pass on the livereload server to the child process or is it possible to query for the livereload server that is currently running in the child process so that I don't create it again getting an already in use error for the port.
the same case with node http server. can I know if the server is already running and use that instead of creating new one.
is it possible to query for the livereload - it is possible and may be implemented in more than one way.
Use stdout/stdin to communicate with the child process. For detailed description look HERE. Basically you can send messages from one process to the other and reply to them.
Use http.request to check if the port is in use.
You can use a file: the process with the server keeps the file open in the write mode - the content of the file stores the port on which the server runs (if needed).
You can use sockets for inter-process communication, as well.
Basically, none of the above guarantees 100% confidentiality, so you have to try/catch for errors anyway: the server may die just after your check, but before you wanted to do something with it.
how to pass on the livereload server to the child process - if you mean sharing an object between different process that it is for sure out of question; if you mean changing the ownership of the object that I am some 99,99% sure it is not possible neither.
What is the problem with having just one process responsible for running the server? And why not to use, let say, forever to take care of running and restarting the server, if needed?
I hope anyone could help me with this issue.
In our company we are setting up a node.js server, connected to a Java Push server.
I'm using https module instead of http and SLL certificates.
The connection between node and clients is made by socket.io, in server and client.
At the same time the node.js server is client of the java server, this connection is being made with regular sockets (net.connect).
The idea is that users connect to the server, join some channels, and when some data arrive from java server, this is dispatched to the corresponding users.
Everything seems to work fine, but after a while, like randomly, having like between 450 and 700 users, the server's CPU reaches 100%, all the connections are broken, but the server is not crashed. The thing is that if you go to the https://... in the browser, you are not getting 404 or something like that but SSL connection error, and its really fast.
I tried to add logs everywhere, but there's not something like a pattern, its like random.
If anybody have the same problem or could bring me a clue, or a tip to debug better, I'll appreciate anything.
Thanks a lot.
Okay, the problem is solved. It is a problem that will occur in every Linux server. So, if you are working with one of these, you need to read this.
The reason was the default limit of files the Linux server had per each process.
Seems that ever single linux server comes with this limitation of 1024 files opened by each process, you can check your limit with:
# ulimit -n
To increase this number
# ulimit -n 5000 (for example)
Each socket creates a new virtual file.
For some reason my server was not displaying any error, the server just got frozen, stopping the log and no signal or evidence of anything. It was when I set up a copy of the server in another machine, when it started to send
warn: error raised: Error: accept EMFILE
warn: error raised: Error: accept EMFILE
warn: error raised: Error: accept EMFILE
...
Be careful because if you are not root, you will only change this for the current session and not permanently.
Trick: If you want to cound the number of files, in this case, the number of files opened by your node process, take note of your process id and call this command.
# ls -l /proc/XXXXX/fd | wc -l
Where XXXXX is the process id. This will help you to know if this is your problem, once you launch your node server, you can use this command to check if it reaches a top, and it stops growing after it gets frozen. (by default 1024 or "ulimit -n").
If you only want to check which files are open by the process:
# ls -l /proc/XXXXX/fd
Hope this can help you. Any way if you are setting up a node js server I'm pretty sure you want to do that to be sure it won't melt.
Finally if you need help in future errors without log, you can try to straceing or dtrussing process
# strace -p <process-id>
should do the job.