How do I prevent node.js from crashing? try-catch doesn't work
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
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
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
, usedomains
withcluster
instead. If you do useuncaughtException
, 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);
});