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Middleware for express applications that checks if the process is taking too long to respond to requests. If so, it skips further requests until the server is able to properly handle them again, protecting the app from crashing during high load peaks.

This is just a wrapper for Lloyd Hilaiel's toobusy module, which is, in fact, the responsible for all the load-handling logic.


npm install --save toobusy-middleware

NOTE: There may be some issues getting toobusy to work in Windows environments. If that's your case and you just want to get it working for development, you can make toobusy an optionalDependency in the package.json and the middleware will act as a noop.

In your application:

var express = require('express');
var toobusy = require('toobusy-middleware');
var app = express();
  // Put toobusy as high as possible in your middleware stack 
var server = app.listen(3000);
process.on('SIGINT', function () {
  // `toobusy`'s shutdown method is exposed by the middleware 


The middleware accepts two parameters:

  • handler (optional): A function that will be called before sending any headers, allowing you to customize how the request is handled. Use this to call external services (bring more nodes up, notify someone, etc) or to override the default response sent to the user.

  • options (optional): Middleware's settings:

    • maxLag: Maximum time (in ms) the server can be behind before the process is considered to be overloaded. See [toobusy's tunable parameters] maxlag for more info.

    • message: Message to be displayed/returned when the server is too busy to process the request. If it's an object or an array, the response will be sent as JSON. Otherwise, it's sent as 'text/html'.

    • status: HTTP status code to send when the server is too busy. Defaults to status code 503 (Service Unavailable).


Uses default behavior.


Simple customization:

  maxLag : 100,
  message : 'Woah! Too busy here! Try again later.',
  status : 500

Sending a JSON response instead of HTML:

  message : {
    message : 'Too busy!',
    solution : 'Try again later...'

Taking action during high load:

// Sends the default response after taking the required action 
app.use(toobusy(function () {

Overriding the default response:

app.use(toobusy(function (req, res, next) {

Using both handler and options:

function notifySomeone() {
app.use(toobusy(notifySomeone, {
  maxLag : 75


This project is licensed under the MIT license. See the LICENSE file for more details.