In my server.js file i'm trying to log errors and not cause them to crash the app, this is the code im using
const server = app.listen(3000, () =>
console.log('Server Up and running')
);
process.on('unhandledRejection', (err, promise) => {
console.log(`Error: ${err}`);
server.close(() => process.exit(1));
})
when i produce an error instead of it logging the error and closing the server it just logs the error how it normally would and causes the app to crash. If you need more info let me know. Sorry if this is a dumb question
I suppose you know the difference between Unhandled Rejection and Uncaught Exception.
it just logs the error how it normally would
Because you're console logging the same error object!
Also don't use process.exit(). Because you might lose your logs. read more
Express docs explained how to do graceful shutdown, you can use similar approach.
I'm using Winston to log to file / seq information I specifically log using log.info or some other level. But I've noticed that when an unhandled exception occurs, it's not logged... I'm not really familiar with Nodejs and HAPI (need to perform some activity while my colleagues are on vacation).. but I was wondering if there's a sort of middleware where I can attach and let Winston log all HAPI stuff.
Thanks in advance
You can listen on uncaughtException and/or unhandledRejection of your current Node.js process to call you logger (here I simply called console.log):
process.on('uncaughtException', (err, origin) => {
console.log('Caught exception:', err, 'Exception origin:', origin);
});
process.on('unhandledRejection', (reason, promise) => {
console.log('Unhandled Rejection at:', promise, 'reason:', reason);
});
However:
uncaughtException is a crude mechanism for exception handling intended to be used only as a last resort.
...
The correct use of uncaughtException is to perform synchronous cleanup of allocated resources (e.g. file descriptors, handles, etc) before shutting down the process. It is not safe to resume normal operation after uncaughtException.
Read also Catch all uncaughtException for Node js app.
In my production env when an error is thrown in a docker container, it just kills the container but doesn't log the error. the only way I can log that error is to warp all the code in the index file with try-catch and then console it.
Does anyone know how costly it is performance-wise to warp all the code in a try-catch block in Nodejs?
I don't see any performance degradation when you wrap it in try..catch. Infact it is a best practice to handle your errors. Not handling means you are prone to errors and unexpected shut down of your applications. You should also have a look why the error is coming and try to fix the root problem. You can also take help of
inbuilt unhandledRejection listener to see all your unhandled errors.
process.on('unhandledRejection', (reason, promise) => {
console.log('Unhandled Rejection at:', promise, 'reason:', reason);
// Application specific logging, throwing an error, or other logic here
});
https://nodejs.org/api/process.html#process_event_unhandledrejection
I build a server which get many requests and response to them.
In some cases, there is an error which cause the server to crush:
events.js:72
throw er; // Unhandled 'error' event
^
Error: ENOENT, open '/mnt/ace/0/file'
I have two problems:
the stack trace doesn't give me any information about the line in my application that cause this exception (I can't do manually debugging because it happens just when I get 1000 request or more).
I don't want that my server ould crush. I prefer that it will raise an exception, but will continue to work.
What the best implementation for this?
You can listen for that kind of stuff and not have it crash the app, but that's not always a great idea.
process.on('uncaughtException', function(err) {
console.log('Something bad happened');
console.log(err.stack);
});
In your case, have you tried checking ulimit settings? You may be having problems opening file handles under loads of 1000+.
Another way of thinking about this is to use domains (if you're using >= 0.8). Domains give you a finer grain of control over how you handle errors based on what contexts cause them.
var domain = require('domain').create();
domain.on('error', function(err) {
console.log(err);
});
domain.run(function() {
// Your code that might throw
});
From my experience, a php server would throw an exception to the log or to the server end, but node.js just simply crashes. Surrounding my code with a try-catch doesn't work either since everything is done asynchronously. I would like to know what does everyone else do in their production servers.
PM2
First of all, I would highly recommend installing PM2 for Node.js. PM2 is really great at handling crash and monitoring Node apps as well as load balancing. PM2 immediately starts the Node app whenever it crashes, stops for any reason or even when server restarts. So, if someday even after managing our code, app crashes, PM2 can restart it immediately. For more info, Installing and Running PM2
Other answers are really insane as you can read at Node's own documents at http://nodejs.org/docs/latest/api/process.html#process_event_uncaughtexception
If someone is using other stated answers read Node Docs:
Note that uncaughtException is a very crude mechanism for exception handling and may be removed in the future
Now coming back to our solution to preventing the app itself from crashing.
So after going through I finally came up with what Node document itself suggests:
Don't use uncaughtException, use domains with cluster instead. If you do use uncaughtException, restart your application after every unhandled exception!
DOMAIN with Cluster
What we actually do is send an error response to the request that triggered the error, while letting the others finish in their normal time, and stop listening for new requests in that worker.
In this way, domain usage goes hand-in-hand with the cluster module, since the master process can fork a new worker when a worker encounters an error. See the code below to understand what I mean
By using Domain, and the resilience of separating our program into multiple worker processes using Cluster, we can react more appropriately, and handle errors with much greater safety.
var cluster = require('cluster');
var PORT = +process.env.PORT || 1337;
if(cluster.isMaster)
{
cluster.fork();
cluster.fork();
cluster.on('disconnect', function(worker)
{
console.error('disconnect!');
cluster.fork();
});
}
else
{
var domain = require('domain');
var server = require('http').createServer(function(req, res)
{
var d = domain.create();
d.on('error', function(er)
{
//something unexpected occurred
console.error('error', er.stack);
try
{
//make sure we close down within 30 seconds
var killtimer = setTimeout(function()
{
process.exit(1);
}, 30000);
// But don't keep the process open just for that!
killtimer.unref();
//stop taking new requests.
server.close();
//Let the master know we're dead. This will trigger a
//'disconnect' in the cluster master, and then it will fork
//a new worker.
cluster.worker.disconnect();
//send an error to the request that triggered the problem
res.statusCode = 500;
res.setHeader('content-type', 'text/plain');
res.end('Oops, there was a problem!\n');
}
catch (er2)
{
//oh well, not much we can do at this point.
console.error('Error sending 500!', er2.stack);
}
});
//Because req and res were created before this domain existed,
//we need to explicitly add them.
d.add(req);
d.add(res);
//Now run the handler function in the domain.
d.run(function()
{
//You'd put your fancy application logic here.
handleRequest(req, res);
});
});
server.listen(PORT);
}
Though Domain is pending deprecation and will be removed as the new replacement comes as stated in Node's Documentation
This module is pending deprecation. Once a replacement API has been finalized, this module will be fully deprecated. Users who absolutely must have the functionality that domains provide may rely on it for the time being but should expect to have to migrate to a different solution in the future.
But until the new replacement is not introduced, Domain with Cluster is the only good solution what Node Documentation suggests.
For in-depth understanding Domain and Cluster read
https://nodejs.org/api/domain.html#domain_domain (Stability: 0 - Deprecated)
https://nodejs.org/api/cluster.html
Thanks to #Stanley Luo for sharing us this wonderful in-depth explanation on Cluster and Domains
Cluster & Domains
I put this code right under my require statements and global declarations:
process.on('uncaughtException', function (err) {
console.error(err);
console.log("Node NOT Exiting...");
});
works for me. the only thing i don't like about it is I don't get as much info as I would if I just let the thing crash.
As mentioned here you'll find error.stack provides a more complete error message such as the line number that caused the error:
process.on('uncaughtException', function (error) {
console.log(error.stack);
});
Try supervisor
npm install supervisor
supervisor app.js
Or you can install forever instead.
All this will do is recover your server when it crashes by restarting it.
forever can be used within the code to gracefully recover any processes that crash.
The forever docs have solid information on exit/error handling programmatically.
Using try-catch may solve the uncaught errors, but in some complex situations, it won't do the job right such as catching async function. Remember that in Node, any async function calls can contain a potential app crashing operation.
Using uncaughtException is a workaround but it is recognized as inefficient and is likely to be removed in the future versions of Node, so don't count on it.
Ideal solution is to use domain: http://nodejs.org/api/domain.html
To make sure your app is up and running even your server crashed, use the following steps:
use node cluster to fork multiple process per core. So if one process died, another process will be auto boot up. Check out: http://nodejs.org/api/cluster.html
use domain to catch async operation instead of using try-catch or uncaught. I'm not saying that try-catch or uncaught is bad thought!
use forever/supervisor to monitor your services
add daemon to run your node app: http://upstart.ubuntu.com
hope this helps!
Give a try to pm2 node module it is far consistent and has great documentation. Production process manager for Node.js apps with a built-in load balancer. please avoid uncaughtException for this problem.
https://github.com/Unitech/pm2
Works great on restify:
server.on('uncaughtException', function (req, res, route, err) {
log.info('******* Begin Error *******\n%s\n*******\n%s\n******* End Error *******', route, err.stack);
if (!res.headersSent) {
return res.send(500, {ok: false});
}
res.write('\n');
res.end();
});
By default, Node.js handles such exceptions by printing the stack trace to stderr and exiting with code 1, overriding any previously set process.exitCode.
know more
process.on('uncaughtException', (err, origin) => {
console.log(err);
});
UncaughtException is "a very crude mechanism" (so true) and domains are deprecated now. However, we still need some mechanism to catch errors around (logical) domains. The library:
https://github.com/vacuumlabs/yacol
can help you do this. With a little of extra writing you can have nice domain semantics all around your code!