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Simple module to warmup a server application (such as an Express app) by hitting server URLs and performing various tasks. This module also allows a worker to be warmed up before it is added to a cluster.


npm install warmup


var warmup = require('warmup');
warmup(app, tasks, callback);
warmup(app, tasks, options, callback);

Simple example of warming up an Express server application:

var warmup = require('warmup');
var express = require('express');
var app = express();
// ... 
        '/foo', // A URL to hit to warmup the server 
        '/bar', // A URL to hit to warmup the server 
            path: '/baz', // Required 
            headers: {
                'User-Agent': 'xxx'
        function myFunc(callback) { // A custom warmup task 
            var port = this.port; // The warmup port is there if you need it 
            name: 'My long task', // You can give a task a name for debugging purposes 
            func: function(callback) {
                setTimeout(function() {
                }, 1200);
            timeout: 2000 // Override the default task timeout 
        timeout: 1000 // Set a default task timeout 
    function(err) {
        if (err) {
            // handle error 

Passing the warmup tasks information:

  • string: as a string that contains the path of the url to make a GET request to during warmup, e.g. '/foo'
  • object: as an object if you want to pass additional properties like headers to the request object. Be sure to pass a path property at the bare minimum when passing the request information in this case

The following options are supported:

  • timeout - Timeout for each task (defaults to 10s)
  • warmupPort - The warmup port to use (defaults to a random port in the range of [10,000-50,000])

The warmup module works by starting the app on a random HTTP port. This allows the application to be started without accepting traffic.


  • All of the tasks are executed in parallel
  • The default timeout is 10s