Day: April 22, 2016

Scheduling jobs on Node.js with node-schedule

Batching is a great part of todays software development. The business world runs on batch from bank statements to promotion emails.

Node.js has some good libraries for such cases.

Node Schedule is a light cron like scheduler for node.

npm install node-schedule

In case your are used to cron and the cron expression format, it will be pretty easy for you. 


var scheduler = require('node-schedule');
 
var montlyJob  = scheduler.scheduleJob('0 0 1 * *', function(){
  console.log('I run the first day of the month');
});

But you also have a javascript object approach

var scheduler = require('node-schedule');

var rule = new scheduler.RecurrenceRule();
rule.hour = 7
rule.dayOfWeek = new schedule.Range(0,6)
 
var dailyJob = schedule.scheduleJob(date, function(){
  console.log('I run on days at 7:00');
});

scheduler.scheduleJob(rule,task);

Also you can have tasks submitted by giving a date

var scheduler = require('node-schedule');

var date = new Date(2017, 1, 1, 0, 0, 0);
var newYearJob = scheduler.scheduleJob(date, function() {
    console.log("Happy new year");
});

However in case your job is not needed you can cancel it pretty easy


newYearJob.cancel();
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Systemd and Upstart Services

Most linux servers that I use are either Debian based or RedHat based.

A common task is adding daemon services.

Suppose that we want to start a tomcat application on startup

First we shall install tomcat

mkdir /opt/tomcat
groupadd tomcat
useradd -s /bin/false -g tomcat -d /opt/tomcat tomcat
wget http://apache.cc.uoc.gr/tomcat/tomcat-8/v8.0.33/bin/apache-tomcat-8.0.33.tar.gz
tar xvf apache-tomcat-8.0.33.tar.gz
mv apache-tomcat-8.0.33/* /opt/tomcat
rm -r apache-tomcat-8.0.33 apache-tomcat-8.0.33.tar.gz 
cd /opt/tomcat
chgrp -R tomcat conf
chmod g+rwx conf
chmod g+r conf/*
chown -R tomcat work/ temp/ logs/

In case of Systemd we should add a tomcat.service file on /etc/systemd/system.
The file /etc/systemd/system/tomcat.service shall contain

[Unit]
Description=Apache Tomcat Web Application Container
After=syslog.target network.target

[Service]
Type=forking

Environment=JAVA_HOME=/usr/java/default
Environment=CATALINA_PID=/opt/tomcat/temp/tomcat.pid
Environment=CATALINA_HOME=/opt/tomcat
Environment=CATALINA_BASE=/opt/tomcat
Environment='CATALINA_OPTS=-Xms512M -Xmx1024M -server -XX:+UseParallelGC'
Environment='JAVA_OPTS=-Duser.timezone=UTC -Djava.awt.headless=true -Djava.security.egd=file:/dev/./urandom'

ExecStart=/opt/tomcat/bin/startup.sh
ExecStop=/bin/kill -15 $MAINPID

User=tomcat
Group=tomcat

[Install]
WantedBy=multi-user.target

I specified the script to start after syslog and network are enabled
As we can see systemd handles the tomcat as a daemon and kills the pid.
With User and Group we specify the user and the group that the process should be run as.
Systemd will handle the upstart process and kill it using the PID.

to enable and run you have to issue 

systemctl enable tomcat
systemctl start tomcat

In case of upstart we should create a tomcat.conf file in /etc/init/
The content of /etc/init/tomcat.conf

description     "Tomcat instance"
author          "Emmanouil Gkatziouras"

respawn
respawn limit 2 5

start on runlevel [2345]
stop on runlevel [!2345]

setuid tomcat
setgid tomcat

env CATALINA_HOME=/opt/tomcat

script
        $CATALINA_HOME/bin/catalina.sh run
end script

post-stop script
        rm -rf $CATALINA_HOME/temp/*
end script

It will start on run levels 2,3,4 or 5
The group and the user id to be executed would be tomcat
After tomcat is stopped the post script block will remove the temp files.
Instead of starting the process inn the background as a daemon,, upstart will handle the process on the foreground.

To start just issue

sudo initctl start tomcat