Hart Hoover

So true

Dual monitors! (via Reddit)

This should be required reading before you buy a domain, with a quiz afterward.

This post describes how to use lsyncd as a syncing mechanism for multiple web servers’ document roots. It’s assumed you are working on CentOS 5 servers.

What is lsyncd?

From the site: Lsyncd watches a local directory trees event monitor interface (inotify). It aggregates and combines events for a few seconds and then spawns one (or more) process(es) to synchronize the changes.

Step One: Set up the file systems for syncing

Let’s say we have two web servers - web-admin and web2. The web-admin server will be the master server that pushes updates to web2. Any update to web2 will be wiped. We want to sync /var/www/html from web-admin to web2.

Step Two: Set up SSH keys between the servers

Here’s a step-by-step on this.

Step Three: Install packages

# yum install lua lua-devel rsync pkgconfig

These are needed for lsyncd. Once you have the prerequisites in place, go get lsyncd from the Google Code page and ./configure && make && make install. Fun times.

Step Four: Configure lsyncd to start on boot

Here’s an init script:

#!/bin/bash
    #
    # lsyncd: Starts the lsync Daemon
    #
    # chkconfig: 345 99 90
    # description: Lsyncd uses rsync to synchronize local directories with a remote
    # machine running rsyncd. Lsyncd watches multiple directories
    # trees through inotify. The first step after adding the watches
    # is to, rsync all directories with the remote host, and then sync
    # single file buy collecting the inotify events.
    # processname: lsyncd

    . /etc/rc.d/init.d/functions

    config="/etc/lsyncd.lau"
    lsyncd="/usr/local/bin/lsyncd"
    lockfile="/var/lock/subsys/lsyncd"
    prog="lsyncd"
    RETVAL=0

    start() {
        if [ -f $lockfile ]; then
        echo -n $"$prog is already running: "
        echo
        else
        echo -n $"Starting $prog: "
        daemon $lsyncd $config
        RETVAL=$?
        echo
        [ $RETVAL = 0 ] && touch $lockfile
        return $RETVAL
        fi
    }

    stop() {
        echo -n $"Stopping $prog: "
        killproc $lsyncd
        RETVAL=$?
        echo
        [ $RETVAL = 0 ] && rm -f $lockfile
        return $RETVAL
    }

    case "$1" in
        start)
        start
        ;;
        stop)
        stop
        ;;
        restart)
        stop
        start
        ;;
        status)
        status $lsyncd
        ;;
        *)

        echo "Usage: lsyncd {start|stop|restart|status}"
        exit 1
    esac

    exit $?

The configuration file is set to /etc/lsyncd.lau, replacing the 10.x.x.x address with your remote host IP:

settings = {
   logfile    = "/var/log/lsyncd/lsyncd.log",
   statusFile = "/var/log/lsyncd/lsyncd-status.log",
   statusInterval = 20

}

sync{
	default.rsyncssh,
	source="/var/www/html",
	host="10.x.x.x",
	targetdir="/var/www/html",
	rsyncOps="-avz"

}

Next, start the service and away you go! You may want to add the lsyncd logs to logrotate. Happy syncing!