mongo-scaled-scheduler

This project allows you to schedule jobs to be run across a cluster of NodeJS services, where you want to ensure only 1 job is triggered at a time.

Installation

npm install --save mongo-scaled-scheduler

Getting Started

import { MongoClient } from 'mongodb';
import createScheduler from 'mongo-scaled-scheduler';

const mongoDbUrl = 'mongodb://localhost:27017/mydatabase';
const client = await MongoClient.connect(mongoDbUrl);
const db = client.db();

const scheduler = await createScheduler({
  collection: db.collection('scheduler'),
});

Examples

Immediate

This will run immediately on a random running instance

scheduler.addJob(async function () {
  const notes = db.collection('notes');
  await notes.insertOne({ test: Date.now() });
});

Set time

This will run once in 10 seconds time.

scheduler.addJob(async function () {
  const notes = db.collection('notes');
  await notes.insertOne({ test: Date.now() });
}, { time: Date.now() + 10000 });

Set interval

This will run in 10 seconds time, and then again every 10 seconds.

scheduler.addJob(async function () {
  const notes = db.collection('notes');
  await notes.insertOne({ test: Date.now() });
}, { interval: 10000 });

Immediate and interval

This will run immediatly and then again every 10 seconds.

scheduler.addJob(async function () {
  const notes = db.collection('notes');
  await notes.insertOne({ test: Date.now() });
}, { time: Date.now(), interval: 10000 });

Remove a job

This will add a job and then remove it.

const jobId = scheduler.addJob(async function () {
  const notes = db.collection('notes');
  await notes.insertOne({ test: Date.now() });
});

scheduler.removeJob(jobId);

Notes

addJob's options are:

• id: a unique id for the job. Will default to a hash of the function stringified
• title: add a title to the mongo document
• time: what time will the job first run?
• interval: milliseconds in which the job will continuously rerun

If id is not provided, then a sha256 hash of the stringified function will be used. This should work in most cases, unless you want to have the same function run multiple jobs. In which case, give each job a unique id.

node crashes during execution

While a scheduled job is running, it will update the mongo document every second with a lastPing of the current time. If there is no ping within 10 seconds, then it is assumed the node process crashed mid execution and allow the next interval to run.

job rejects during execution

If a job rejects during execution it will not rerun that try, but if there is an interval it will try again at the next interval.

Error Handling

In case of errors during the execution of a job, the scheduler will emit an 'error' event. You can handle these errors by adding an event listener:

scheduler.on('error', (error) => {
  console.error('An error occurred while executing a job:', error);
});