{"id":8489,"date":"2020-05-22T10:50:02","date_gmt":"2020-05-22T17:50:02","guid":{"rendered":"https:\/\/www.couchbase.com\/blog\/?p=8489"},"modified":"2025-06-13T22:40:23","modified_gmt":"2025-06-14T05:40:23","slug":"implementing-a-robust-portable-cron-like-scheduler-via-couchbase-eventing-part-1","status":"publish","type":"post","link":"https:\/\/www.couchbase.com\/blog\/implementing-a-robust-portable-cron-like-scheduler-via-couchbase-eventing-part-1\/","title":{"rendered":"Implementing a Scheduler Via Couchbase Eventing (Part 1)"},"content":{"rendered":"

This is the first of a multi-part series to leverage the Couchbase Eventing Service<\/a> to run multiple scheduled tasks at specific recurring intervals in a cron<\/em> like fashion completely inside the database without requiring additional infrastructure via a single general-purpose Eventing Function.<\/p>\n

In this installment, we will focus on running fixed user routines, JavaScript functions defined inside an Eventing Function.<\/p>\n

Later in subsequent articles we will extend the cron<\/em> like Eventing Function to schedule and execute database driven dynamic N1QL statements and then finally in we will explore scheduling database driven dynamic JavaScript functions.<\/p>\n

Background<\/h3>\n

The Couchbase Eventing Service provides a framework for writing your own routines, simple JavaScript functions, to process document changes. \u00a0This service provides all the needed infrastructure to create scalable and robust cloud-based functions allowing you to focus on developing pure business logic to interact in near real-time to changes in your data. Your functions are able to access the Couchbase data service (KV), the Couchbase query service (N1QL), and REST endpoints external to the Couchbase system.<\/p>\n

\"Eventing<\/p>\n

The JSON<\/a> data model in Couchbase came from JavaScript<\/a>, thus it is only natural that the Eventing Service exposes the ability to write JavaScript code to analyze and manipulate JSON documents on any type of change events including Inserts, Updates, Merges, and Deletes (together referred to as mutations).<\/p>\n

Eventing Functions typically allow you to deploy and execute custom code fragments to that react to thousands and even millions of mutations per seconds in your documents. Several typical use cases are documented<\/a> for developing high velocity at-scale Eventing Functions that respond to mutations of Couchbase documents.<\/p>\n

\"Eventing<\/p>\n

This article will focus instead on a very low velocity use case of the Eventing Service building a reliable \u201cin database\u201d distributed crontab, allowing you to execute JavaScript functions that interact with Couchbase services on a regular periodic schedule.<\/p>\n

Scheduling business logic to run at a specified date or time<\/h3>\n

Cron<\/a>, named after \u201cChronos<\/em>,\u201d the Greek word for time is one of the most useful utilities in a Linux system. In Linux the cron<\/em> utility is driven by a crontab (cron table) file, a configuration file that specifies shell commands to run periodically on a given schedule.<\/p>\n

One drawback in running cron<\/em> is that it is not designed to be a distributed service; it runs on single box, as such it presents a single point of failure. If the system is offline for several hours all scheduled tasks are missed.<\/p>\n

Yes, there are some distributed cron<\/em> implementations such as Google\u2019s Cloud Service, AWS\u2019 Scheduled Tasks, and Azure Functions \/ Time Triggers. But each cloud vendors offerings have their own idioms are not directly portable.<\/p>\n

In addition, the methodology of configuration and control needs to be secured, for example if you control a distributed cron<\/em> system via a REST API over HTTP\/S you need to account for this in your security plan.<\/p>\n

Using the Couchbase itself to run periodic commands<\/h3>\n

With a minor amount of code and planning you can leverage Couchbase\u2019s Eventing service to provide flexible cron<\/em> like functionality for your scheduled database operations or maintenance. Building the scheduler into the database allows you to achieve the following benefits:<\/p>\n