@deboxsoft/cron-jobs v0.5.2

Table of Contents

• Foreword
• Install
• Usage and Examples
  • Node
  • Browser
• Node.js Email Queue Job Scheduling Example
• Instance Options
• Job Options
• Job Interval and Timeout Values
• Listening for events
• Custom error handling
• Cancellation, Retries, Stalled Jobs, and Graceful Reloading
• Interval, Timeout, Date, and Cron Validation
• Writing jobs with Promises and async-await
• Callbacks, Done, and Completion States
• Long-running jobs
• Complex timeouts and intervals
• Custom Worker Options
• Using functions for jobs
• Concurrency

Foreword

Previous to creating this, I was relying heavily on bull; having created @ladjs/bull – but due to core issues (and being Redis-backed) it was not the best tool for the job. Bull might have been okay if the core issues were fixed, however since it uses Redis it should not be used for a job queue. From my experience, Redis should only be used for caching and session storage purposes (e.g. CDN or managing user log in state in your application). As of the time of this writing, it has been months and the core bugs with Bull are still unresolved; as more people are continuing to reproduce and comment on the known issues.

Since workers are now readily available in LTS versions of Node, I thought it would be a great time to implement them in a job scheduler environment. Additionally, my research and development of a better anti-spam and anti-phishing classifier with Spam Scanner gave me some necessary insight to using workers.

CronJobs was created to give you fine-grained control with simplicity, and has built-in support for workers, sandboxed processes, graceful reloading, cron jobs, dates, human-friendly time representations, and much more. We recommend you to query a persistent database in your jobs, to prevent specific operations from running more than once. CronJobs does not force you to use an additional database layer of Redis or MongoDB to manage job state. In doing so, you should manage boolean job states yourself using queries. For instance, if you have to send a welcome email to users, only send a welcome email to users that do not have a Date value set yet for welcome_email_sent_at.

Install

npm:

npm install @deboxsoft/cron-jobs

yarn:

yarn add @deboxsoft/cron-jobs

Usage and Examples

The example below assumes that you have a directory jobs in the root of the directory from which you run this example. For example, if the example below is at /path/to/script.js, then /path/to/jobs/ must also exist as a directory. If you wish to disable this feature, then pass root: false as an option.

Inside this jobs directory are individual scripts which are run using Workers per optional timeouts, and additionally, an optional interval or cron expression. The example below contains comments, which help to clarify how this works.

The option jobs passed to a new instance of CronJobs (as shown below) is an Array. It contains values which can either be a String (name of a job in the jobs directory, which is run on boot) OR it can be an Object with name, path, timeout, and interval properties. If you do not supply a path, then the path is created using the root directory (defaults to jobs) in combination with the name. If you do not supply values for timeout and/nor interval, then these values are defaulted to 0 (which is the default for both, see index.js for more insight into configurable default options).

We have also documented all Instance Options and Job Options in this README below. Be sure to read those sections so you have a complete understanding of how CronJobs works.

Node

Since we use bthreads, Node v10+ is supported. For versions prior to Node v11.7.0, a ponyfill is provided for workers that uses child_process. For versions greater than or equal to Node v11.7.0, it uses workers directly. You can also pass --experimental-worker flag for older versions to use worker_threads (instead of the child_process polyfill). See the official Node.js documentation for more information.

NOTE: If you are using Node versions prior to Node v11.7.0, then in your worker files – you will need to use bthreads instead of workers. For example, you will const thread = require('bthreads'); at the top of your file, instead of requiring worker_threads. This will also require you to install bthreads in your project with npm install bthreads or yarn add bthreads.

const path = require('path');

// optional
const ms = require('ms');
const dayjs = require('dayjs');
const Graceful = require('@ladjs/graceful');
const Cabin = require('cabin');

// required
const CronJobs = require('@deboxsoft/cron-jobs');

//
// NOTE: see the "Instance Options" section below in this README
// for the complete list of options and their defaults
//
const cronJobs = new CronJobs({
  //
  // NOTE: by default the `logger` is set to `console`
  // however we recommend you to use CabinJS as it
  // will automatically add application and worker metadata
  // to your log output, and also masks sensitive data for you
  // <https://cabinjs.com>
  //
  logger: new Cabin(),

  //
  // NOTE: instead of passing this Array as an option
  // you can create a `./jobs/index.js` file, exporting
  // this exact same array as `module.exports = [ ... ]`
  // doing so will allow you to keep your job configuration and the jobs
  // themselves all in the same folder and very organized
  //
  // See the "Job Options" section below in this README
  // for the complete list of job options and configurations
  //
  jobs: [
    // runs `./jobs/foo.js` on start
    'foo',

    // runs `./jobs/foo-bar.js` on start
    {
      name: 'foo-bar'
    },

    // runs `./jobs/some-other-path.js` on start
    {
      name: 'beep',
      path: path.join(__dirname, 'jobs', 'some-other-path')
    },

    // runs `./jobs/worker-1.js` on the last day of the month
    {
      name: 'worker-1',
      interval: 'on the last day of the month'
    },

    // runs `./jobs/worker-2.js` every other day
    {
      name: 'worker-2',
      interval: 'every 2 days'
    },

    // runs `./jobs/worker-3.js` at 10:15am and 5:15pm every day except on Tuesday
    {
      name: 'worker-3',
      interval: 'at 10:15 am also at 5:15pm except on Tuesday'
    },

    // runs `./jobs/worker-4.js` at 10:15am every weekday
    {
      name: 'worker-4',
      cron: '15 10 ? * *'
    },

    // runs `./jobs/worker-5.js` on after 10 minutes have elapsed
    {
      name: 'worker-5',
      timeout: '10m'
    },

    // runs `./jobs/worker-6.js` after 1 minute and every 5 minutes thereafter
    {
      name: 'worker-6',
      timeout: '1m',
      interval: '5m'
      // this is unnecessary but shows you can pass a Number (ms)
      // interval: ms('5m')
    },

    // runs `./jobs/worker-7.js` after 3 days and 4 hours
    {
      name: 'worker-7',
      // this example uses `human-interval` parsing
      timeout: '3 days and 4 hours'
    },

    // runs `./jobs/worker-8.js` at midnight (once)
    {
      name: 'worker-8',
      timeout: 'at 12:00 am'
    },

    // runs `./jobs/worker-9.js` every day at midnight
    {
      name: 'worker-9',
      interval: 'at 12:00 am'
    },

    // runs `./jobs/worker-10.js` at midnight on the 1st of every month
    {
      name: 'worker-10',
      cron: '0 0 1 * *'
    },

    // runs `./jobs/worker-11.js` at midnight on the last day of month
    {
      name: 'worker-11',
      cron: '0 0 L * *'
    },

    // runs `./jobs/worker-12.js` at a specific Date (e.g. in 3 days)
    {
      name: 'worker-12',
      // <https://github.com/iamkun/dayjs>
      date: dayjs().add(3, 'days').toDate()
      // you can also use momentjs
      // <https://momentjs.com/>
      // date: moment('1/1/20', 'M/D/YY').toDate()
      // you can pass Date instances (if it's in the past it will not get run)
      // date: new Date()
    },

    // runs `./jobs/worker-13.js` on start and every 2 minutes
    {
      name: 'worker-13',
      interval: '2m'
    },

    // runs `./jobs/worker-14.js` on start with custom `new Worker` options (see below)
    {
      name: 'worker-14',
      // <https://nodejs.org/api/worker_threads.html#worker_threads_new_worker_filename_options>
      worker: {
        workerData: {
          foo: 'bar',
          beep: 'boop'
        }
      }
    },

    // runs `./jobs/worker-15.js` **NOT** on start, but every 2 minutes
    {
      name: 'worker-15',
      timeout: false, // <-- specify `false` here to prevent default timeout (e.g. on start)
      interval: '2m'
    },

    // runs `./jobs/worker-16.js` on January 1st, 2022
    // and at midnight on the 1st of every month thereafter
    {
      name: 'worker-16',
      date: dayjs('1-1-2022', 'M-D-YYYY').toDate(),
      cron: '0 0 1 * *'
    }
  ]
});

// handle graceful reloads, pm2 support, and events like SIGHUP, SIGINT, etc.
const graceful = new Graceful({ cronJobss: [cronJobs] });
graceful.listen();

// start all jobs (this is the equivalent of reloading a crontab):
cronJobs.start();

/*
// start only a specific job:
cronJobs.start('foo');

// stop all jobs
cronJobs.stop();

// stop only a specific job:
cronJobs.stop('beep');

// run all jobs (this does not abide by timeout/interval/cron and spawns workers immediately)
cronJobs.run();

// run a specific job (...)
cronJobs.run('beep');

// add a job array after initialization:
cronJobs.add(['boop']);
// this must then be started using one of the above methods

// add a job after initialization:
cronJobs.add('boop');
// this must then be started using one of the above methods

// remove a job after initialization:
cronJobs.remove('boop');
*/

Browser

NOTE: Browser support is currently unstable until this GitHub issue is resolved. Contributions are welcome!

If you are using CronJobs in the browser, then please reference the Web Workers API (since it does not use Node.js worker threads). If the Web Workers API is not yet available, then it will be polyfilled accordingly.

VanillaJS

This is the solution for you if you're just using <script> tags everywhere!

<script src="https://unpkg.com/cronJobs"></script>
<script>
  (function () {
    function hello() {
      console.log('hello');
      postMessage('done');
    }

    const cronJobs = new JobWorkerManager({
      jobs: [
        {
          name: 'hello',
          path: hello,
          interval: '5s',
        }
      ]
    });

    cronJobs.start();
  })();
</script>

Bundler

Assuming you are using browserify, webpack, rollup, or another bundler, you can simply follow Node usage above.

Node.js Email Queue Job Scheduling Example

A very common use case for a Node.js job scheduler is the sending of emails.

We highly recommend you to use CronJobs in combination with the email-templates package (made by the same author). Not only does it let you easily manage email templates, but it also automatically opens email previews in your browser for you during local development (using preview-email).

You will then create in your application a MongoDB "email" collection (or SQL table) with the following properties (or SQL columns):

• template (String) - the name of the email template
• message (Object) - a Nodemailer message object
• locals (Object) - an Object of locals that are passed to the template for rendering

Here are optional properties/columns that you may want to also add (you'll need to implement the logic yourself as the example provided below does not include it):

• send_at (Date) - the Date you want to send an email (should default to current Date.now() when record is created, and can be overridden on a per job basis)
• sent_at (Date) - the Date that the email actually got sent (set by your job in CronJobs - you would use this when querying for emails to send, and specifically exclude any emails that have a sent_at value sent in your query)
• response (Object) - the mixed Object that is returned from Nodemailer sending the message (you should store this for historical data and so you can detect bounces)

In your application, you will then need to save a new record into the collection or table (where you want to trigger an email to be queued) with values for these properties.

Lastly, you will need to set up CronJobs to fetch from the email collection every minute (you can configure how frequent you wish, however you may want to implement locking, by setting a is_locked Boolean property, and subsequently unlocking any jobs locked more than X minutes ago – but typically this is not needed unless you are sending thousands of emails and have a slow SMTP transport).

const CronJobs = require('cronJobs');
const Graceful = require('@ladjs/graceful');
const Cabin = require('cabin');

//
// we recommend using Cabin as it is security-focused
// and you can easily hook in Slack webhooks and more
// <https://cabinjs.com>
//
const logger = new Cabin();

const cronJobs = new CronJobs({
  logger,
  jobs: [
    {
      // runs `./jobs/email.js` on start and every minute
      name: 'email',
      interval: '1m'
    }
  ]
});

Example contents of a file named ./jobs/email.js:

const os = require('os');
const { parentPort } = require('worker_threads');

const Cabin = require('cabin');
const Email = require('email-templates');
const pMap = require('p-map');

//
// we recommend using Cabin as it is security-focused
// and you can easily hook in Slack webhooks and more
// <https://cabinjs.com>
//
const logger = new Cabin();

//
// we recommend using email-templates to
// create, send, and manage your emails
// <https://email-templates.js.org>
//
const email = new Email({
  message: {
    // set a default from that will be set on all messages
    // (unless you specifically override it on an individual basis)
    from: 'elon@tesla.com'
  }
});

// store boolean if the job is cancelled
let isCancelled = false;

// how many emails to send at once
const concurrency = os.cpus().length;

// example database results
const results = [
  {
    template: 'welcome',
    message: {
      to: 'elon@spacex.com'
    },
    locals: {
      foo: 'bar',
      beep: 'boop'
    }
  }
  // ...
];

async function mapper(result) {
  // return early if the job was already cancelled
  if (isCancelled) return;
  try {
    const response = await email.send(result);
    logger.info('sent email', { response });
    // here is where you would write to the database that it was sent
    return response;
  } catch (err) {
    // catch the error so if one email fails they all don't fail
    logger.error(err);
  }
}

// handle cancellation (this is a very simple example)
if (parentPort)
  parentPort.once('message', message => {
    //
    // TODO: once we can manipulate concurrency option to p-map
    // we could make it `Number.MAX_VALUE` here to speed cancellation up
    // <https://github.com/sindresorhus/p-map/issues/28>
    //
    if (message === 'cancel') isCancelled = true;
  });

(async () => {
  // query database results for emails not sent
  // and iterate over them with concurrency
  await pMap(results, mapper, { concurrency });

  // signal to parent that the job is done
  if (parentPort) parentPort.postMessage('done');
  else process.exit(0);
})();

Example contents of a file named ./emails/welcome/html.pug:

p Welcome to Tesla
ul
  li
    strong Foo value:
    = ' '
    = foo
  li
    strong Beep value:
    = ' '
    = beep

Example contents of a file named ./emails/welcome/subject.pug:

= 'Welcome to Tesla'

NOTE: We have provided a complete demo example using Express at https://github.com/cronJobsjs/express-example.

Instance Options

Here is the full list of options and their defaults. See index.js for more insight if necessary.

Job Options

See Interval, Timeout, Date, and Cron Validate below for more insight besides this table:

Job Interval and Timeout Values

These values can include Number, Object, and String variable types:

• Number values indicates the number of milliseconds for the timeout or interval
• Object values must be a later schedule object value (e.g. later.parse.cron('15 10 * * ? *')))
• String values can be either a later, human-interval, or ms String values (e.g. later supports Strings such as every 5 mins, human-interval supports Strings such as 3 days and 4 hours, and ms supports Strings such as 4h for four hours)

Listening for events

CronJobs extends from EventEmitter and emits two events:

• worker created with an argument of name
• worker deleted with an argument of name

If you'd like to know when your workers are created (or deleted), you can do so through this example:

cronJobs.on('worker created', (name) => {
  console.log('worker created', name);
  console.log(cronJobs.workers[name]);
});

cronJobs.on('worker deleted', (name) => {
  console.log('worker deleted', name);
  console.log(typeof cronJobs.workers[name] === 'undefined');
});

Custom error handling

If you'd like to override default behavior for worker error handling, provide a callback function as errorHandler parameter when creating a CronJobs instance.

An example use-case. If you want to call an external service to record an error (like Honeybadger, Sentry, etc.) along with logging the error internally. You can do so with:

const logger = ('../path/to/logger');
const errorService = ('../path/to/error-service');

new JobWorkerManager({
  jobs: [
    {
      name: 'job that sometimes throws errors',
      path: jobFunction
    }
  ],
  errorHandler: (error, workerMetadata) => {
    // workerMetadata will be populated with extended worker information only if
    // CronJobs instance is initialized with parameter `workerMetadata: true`
    if (workerMetadata.threadId) {
      logger.info(`There was an error while running a worker ${workerMetadata.name} with thread ID: ${workerMetadata.threadId}`)
    } else {
      logger.info(`There was an error while running a worker ${workerMetadata.name}`)
    }

    logger.error(error);
    errorService.captureException(error);
  }
});

Cancellation, Retries, Stalled Jobs, and Graceful Reloading

We recommend that you listen for "cancel" event in your worker paths. Doing so will allow you to handle graceful cancellation of jobs. For example, you could use p-cancelable

Here's a quick example of how to do that (e.g. ./jobs/some-worker.js):

// <https://nodejs.org/api/worker_threads.html>
const { parentPort } = require('worker_threads');

// ...

function cancel() {
  // do cleanup here
  // (if you're using @ladjs/graceful, the max time this can run by default is 5s)

  // send a message to the parent that we're ready to terminate
  // (you could do `process.exit(0)` or `process.exit(1)` instead if desired
  // but this is a bit of a cleaner approach for worker termination
  if (parentPort) parentPort.postMessage('cancelled');
  else process.exit(0);
}

if (parentPort)
  parentPort.once('message', message => {
    if (message === 'cancel') return cancel();
  });

If you'd like jobs to retry, simply wrap your usage of promises with p-retry.

We leave it up to you to have as much fine-grained control as you wish.

See @ladjs/graceful for more insight into how this package works.

Interval, Timeout, Date, and Cron Validation

If you need help writing cron expressions, you can reference crontab.guru.

We support later, human-interval, or ms String values for both timeout and interval.

If you pass a cron property, then it is validated against cron-validate.

You can pass a Date as the date property, but you cannot combine both date and timeout.

If you do pass a Date, then it is only run if it is in the future.

See Job Interval and Timeout Values above for more insight.

Writing jobs with Promises and async-await

If jobs are running with Node pre-v14.8.0, which enables top-level async-await support, here is the working alternative:

const { parentPort } = require('worker_threads');

const delay = require('delay');
const ms = require('ms');

(async () => {
  // wait for a promise to finish
  await delay(ms('10s'));

  // signal to parent that the job is done
  if (parentPort) parentPort.postMessage('done');
  else process.exit(0);
})();

Callbacks, Done, and Completion States

To close out the worker and signal that it is done, you can simply parentPort.postMessage('done'); and/or process.exit(0).

While writing your jobs (which will run in worker threads), you should do one of the following:

• Signal to the main thread that the process has completed by sending a "done" message (per the example above in Writing jobs with Promises and async-await)
• Exit the process if there is NOT an error with code 0 (e.g. process.exit(0);)
• Throw an error if an error occurs (this will bubble up to the worker event error listener and terminate it)
• Exit the process if there IS an error with code 1 (e.g. process.exit(1))

Long-running jobs

If a job is already running, a new worker thread will not be spawned, instead logger.error will be invoked with an error message (no error will be thrown, don't worry). This is to prevent bad practices from being used. If you need something to be run more than one time, then make the job itself run the task multiple times. This approach gives you more fine-grained control.

By default, workers run indefinitely and are not closed until they exit (e.g. via process.exit(0) or process.exit(1), OR send to the parent port a "close" message, which will subsequently call worker.close() to close the worker thread.

If you wish to specify a maximum time (in milliseconds) that a worker can run, then pass closeWorkerAfterMs (Number) either as a default option when creating a new CronJobs() instance (e.g. new CronJobs({ closeWorkerAfterMs: ms('10s') })) or on a per-job configuration, e.g. { name: 'beep', closeWorkerAfterMs: ms('5m') }.

As of v6.0.0 when you pass closeWorkerAfterMs, the timer will start once the worker is signaled as "online" (as opposed to previous versions which did not take this into account).

Complex timeouts and intervals

Since we use later, you can pass an instance of later.parse.recur, later.parse.cron, or later.parse.text as the timeout or interval property values (e.g. if you need to construct something manually).

You can also use dayjs to construct dates (e.g. from now or a certain date) to millisecond differences using dayjs().diff(new Date(), 'milliseconds'). You would then pass that returned Number value as timeout or interval as needed.

Custom Worker Options

You can pass a default worker configuration object as new CronJobs({ worker: { ... } });.

These options are passed to the options argument when we internally invoke new Worker(path, options).

Additionally, you can pass custom worker options on a per-job basis through a worker property Object on the job definition.

See complete documentation for options (but you usually don't have to modify these).

Using functions for jobs

It is highly recommended to use files instead of functions. However, sometimes it is necessary to use functions.

You can pass a function to be run as a job:

new JobWorkerManager({jobs: [someFunction]});

(or)

new JobWorkerManager({
  jobs: [
    {
      name: 'job with function',
      path: someFunction
    }
  ]
});

The function will be run as if it's in its own file, therefore no variables or dependencies will be shared from the local context by default.

You should be able to pass data via worker.workerData (see Custom Worker Options).

Note that you cannot pass a built-in nor bound function.

Concurrency

We recommend using the following packages in your workers for handling concurrency:

• https://github.com/sindresorhus/p-all
• https://github.com/sindresorhus/p-limit
• https://github.com/sindresorhus/p-queue
• https://github.com/sindresorhus/p-map