Express: Error: connect ECONNRESET

[RussellRC]

I have an express server running on localhost through app.listen().
It serves images through app.get('imageId'). The images are read from a DB.
I have a client application firing 400+ requests at the same time through http.get()

After the first 300+ requests, I get this error on the client side for each subsequent request:
Error: connect ECONNRESET 127.0.0.1:8080
There is no stack or any further detail.

On the server side, I have these error handlers, but none of them print anything:

server.on('error', function(err){
    console.error('on error handler');
    console.error(err);
});
server.on('clientError', function(err){
    console.error('on clientError handler');
    console.error(err);
});
process.on('uncaughtException', function(err) {
    console.error('process.on handler');
    console.error(err);
});

My guess is that the server is not able to handle all the requests at once and it starts rejecting the connections until it frees resources, but haven't found a way to prove it.

Is there a way to specify the number of connections on the server?
Am I doing something wrong on the server side to handle the error?

[michaelBenin]

Check your code for an error piping a stream to res. I've run into the same issue and that was the cause. Hope this helps.

Also, this error might be better for stackoverflow.

[RussellRC]

Thanks @michaelBenin,

Is there a way to set the number of max connections in express?

[dougwilson]

Hi @RussellRC all the app.listen() is is a short-cut to the Node.js HTTP server creation + listen. Do you see the same behavior if you replace your app.listen(port) with the following?

require('http').createServer(app).listen(port)

If so, this is likely an issue with Node.js directly.

For max connections, as far as I know, there is no maximum defined to even change.

[michaelBenin]

You can set global max sockets in http and https packages. I could help you debug if I could see the middleware. Could you show us some of the controllers/middleware/route handlers used? There is a broken pipe somewhere though. Try using a try catch around some of your stream logic.

[RussellRC]

Hi @dougwilson. I tried what you said and I get the same error.

On the other hand, I created a client on Java that does the same as my client on NodeJS: fires 400+ concurrent requests, each one getting a different image from the server, and it worked just fine, so now I suspect the problem is on my NodeJS client.

Here is a snippet of what I am doing on the client:

        var srvUrl = url.parse(imgUrl);
        var options = {
                hostname: srvUrl.hostname,
                port: srvUrl.port,
                path: srvUrl.path,
                timeout: 60000
        };

        http.get(options, function(response) {
            var outFile = fs.createWriteStream(outFileName, {flags: 'w', encoding: 'base64'});
            response.pipe(outFile);

            outFile.on('error', function(error) {
                console.log("pipe error on", outFileName);
            });
        }).on('error', function(e) {
            console.error("Got error for '" + imgUrl + "' :" + e);
        }).end();

The error I get (Error: connect ECONNRESET 127.0.0.1:8080) comes from http.get().on('error'), not form the pipe.

[michaelBenin]

@RussellRC are you able to reproduce this with an invalid imgUrl? Try passing something you know will fail. Like I said above, I spent a good amount of time dealing with the same issue with node streams on a few projects.

response.pipe(outFile); with an invalid url or a url that doesn't exist will result with the original error reported, the ECONNRESET. Can you try wrapping response.pipe(outFile); in a try catch? I don't think this is a problem with express.

[RussellRC]

@michaelBenin I did what you suggested and still got the same error, which makes sense because it is happening on the http.get() method, not on the pipe.

However, one thing I just noticed is that the first time I run my script, a few calls on http.get() fail, but on subsequent runs of the script, sometimes all the requests go through. So I agree that this is not a problem with express but rather how http.get() works... I'll do some more digging, but for now I think we can close this issue.

Thanks a lot for the help.

[pszabop]

Ugh, wish this were addressed somewhere. I've got unit tests randomly failing with ECONNRESET and the more functionality I add to the server, the higher frequency of the failures.

[Waog]

I had this Error too and was able to solve it after days of debugging and analysis:

my solution

For me VirtualBox (for Docker) was the Problem. I had Port Forwarding configured on my VM and the error only occured on the forwarded port.

general conclusions

The following observations may save you days of work I had to invest:

• For me the problem only occurred on connections from localhost to localhost on one port. -> check changing any of these constants solves the problem.
• For me the problem only occurred on my machine -> let someone else try it.
• For me the problem only occurred after a while and couldn't be reproduced reliably
• My Problem couldn't be inspected with any of nodes or expresses (debug-)tools. -> don't waste time on this

-> figure out if something is messing around with your network (-settings), like VMs, Firewalls etc., this is probably the cause of the problem.

[Xisabla]

Got this error too, I found why and it's about the port too.
This can happen if you are using a node script watcher like nodemon or a process manager such as pm2

• For nodemon, the previous instance of the script could not be totally "killed" before the new one starts, then you will get 2 servers listening on the same port.
• For pm2, I've just forgotten to close an instance before starting a new one, that's kinda the same thing.

So, if you don't have a port forwarding issue, check for your server instances or if the port isn't taken by another program 😉