redis-schedule

Simple Scheduler Solution for Node based on REDIS.

How to use

npm install redis-schedule --save

planner.js

const scheduler = require('redis-scheduler');
scheduler.connect({ host: 'localhost', port: 6379' });

scheduler.schedule('someJob', 'uniq_key', Date.now());

worker.js

const scheduler = require('redis-scheduler');
scheduler.connect({ host: 'localhost', port: 6379' });

scheduler.worker.register('someJob', (data) => {
  console.log('got data from scheduler');
});

API

"connect"

Redis scheduler use singleton for the connection to REDIS. connect once and you can use it everywhere

scheduler.connect(options)

connect use the same options with redis connect: https://github.com/NodeRedis/node_redis/blob/master/README.md#connect

"schedule"

Schedule a task to run at a specific timestamp.

scheduler.schedule(jobName, key, timestamp);

Parameter

Property	Default	Description
jobName		Name of the Job
key		Identifer of the schedule
timestamp		Unix timestamp where the job should be executed

"cancel"

Cancel a task with a key.

Notes: All the tasks with the same key in the Job will be cancel.

scheduler.cancel(jobName, key);

Parameter

Property	Default	Description
jobName		Name of the Job
key		Identifer of the schedule

Worker

Handle jobs

Register

Register a worker which process the task at the due time.

scheduler.worker.register(jobName, handler, prefetch)

handler = (key) => { // do something with the key}

Property	Default	Description
jobName		Name of the Job
handler		Function to process schedule job
prefetch	5	Number of items to be received for each interval

Cancel

Remove a worker

scheduler.worker.cancel(jobName)

Property	Default	Description
jobName		Name of the Job

Note: Only one worker should exist at once. otherwise, duplicated messages will be processed

Behind the scence

• schedule: ZADD jobName key timestamp
• cancel: ZREM jobName key
• worker:
  • interval get data from redis ZRANGES jobName 0 {prefetch -1} WITHSCORES
  • check if the score is smaller than now
    • If it's true, process message, ZREM jobName key
    • If it's false, ignore it

LIMITATIONS

• This is a very basic version of scheduler. It should be used for small sized application only.
• If you need more advanced feature, go with RabbitMQ with x-delayed-message plugin.
• No ack implemented for worker. Therefore, you have to implement yourself requeue when a job is failed.
• The timestamp is from your application. So make sure the planner and the worker have consistent time.
• The key should be unique, since when we use ZREM jobName key. All duplicated items with that key will be removed.