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How to Create a Scheduler Service in Node.js?
- Authors
- Name
- Emin Vergil
- @eminvergil
Overview
- What is a Scheduler Service?
- How to Write a Node.js Scheduler Service?
- How to Write a systemd Service File
What is a Scheduler Service?
A scheduler service provides the ability to execute tasks at specific times or intervals.
How to Write a Node.js Scheduler Service?
You can write a scheduler service in most modern frameworks, such as .NET Core, Elixir, Node.js, Go, etc.
In this example, I will use Node.js. To follow this example, you need to have basic knowledge of JavaScript.
Take the following steps to create a basic scheduler service:
1. Create a Project Folder for Your Service
mkdir scheduler-service && cd scheduler-service
2. Initialize npm
npm init -y
3. Install the Following Packages:
- node-schedule
- log4js
I chose the node-schedule
package for cron-like scheduling functionality and log4js
for logging.
4. Create a JavaScript File
- Example:
schedule.js
scheduleJob
Function
5. Import the node-schedule Library and Assign a Job to the const schedule = require('node-schedule')
const job = schedule.scheduleJob('*/1 * * * *', function () {
console.log('Every minute, you will see this log.')
})
As you can see in the example above, scheduleJob
has two parameters:
1. Cron Expression
Cron expressions are used to initialize a repetitive time for a job. It is a string consisting of six or seven subexpressions (fields) that describe individual details of the schedule.
┬ ┬ ┬ ┬ ┬ ┬
│ │ │ │ │ │
│ │ │ │ │ └ Day of week (0 - 7) (0 or 7 is Sunday)
│ │ │ │ └───── Month (1 - 12)
│ │ │ └────────── Day of month (1 - 31)
│ │ └─────────────── Hour (0 - 23)
│ └──────────────────── Minute (0 - 59)
└───────────────────────── Second (0 - 59)
2. A Function
This function defines the task that we want to schedule.
Here is the complete JavaScript code that uses log4js
to log:
const log4js = require('log4js')
log4js.configure({
appenders: { log: { type: 'file', filename: 'schedule.log' } },
categories: { default: { appenders: ['log'], level: 'info' } },
})
const logger = log4js.getLogger('log')
logger.info('Scheduler started.')
const job = schedule.scheduleJob('*/1 * * * *', function () {
logger.warn('Every minute, you will see this log.')
})
systemd
Service File
How to Write a To register our service with the Linux service manager, we need to create a systemd
service file.
Take the following steps to create a systemd
service file:
1. Type the Following Command in the Linux Terminal
vi /etc/systemd/system/schedule.service
2. Put the Following Content in It
[Unit]
Description=Node Service
[Service]
WorkingDirectory=/home/emin/node/
User=ubuntu
ExecStart=/usr/bin/node /home/ubuntu/hello_env.js
Restart=on-failure
RestartSec=10
sudo systemctl daemon-reload
3. Run You must do this whenever any of the service files change at all so that systemd
picks up the new information.
4. Start the Service
sudo systemctl start schedule
5. Check the Status of the Service
sudo systemctl status schedule
This command shows the status of the service.
After starting your service, you should see a schedule.log
file in the location of the service.
Resources:
- Run a Node.js App as a Background Service
- node-schedule
- Practical Implementation of .NET Core Background Services
- Node.js App with systemd