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mirroring file system between 3 servers

i have a small network with three servers. the main server is located in Jakarta, and two "sub" servers are located in Bali and Batam.

For a few years now I have been using Unison to keep all the user files on these 3 systems in sync with one another. thus, if a user in Batam changes a file on their local server, then servers in Jakarta and Bali are also updated.

i just use consumer class 3Mbps internet connections for all this.

this system has worked sort of ok, but Unison has its limitations, bugs and problems.

is there any other way i can more reliably keep all these 3 servers in sync?

suggestions very much appreciated.

There is need to know, on which OS you are looking ?
becasue there are many softwares(freeware/Shareware) avalible for the sync. if you have linux you can use "rync" utility.

thanks,

You could try using lsyncd:
http://code.google.com/p/lsyncd/

Quote:

Originally Posted by deepak_message (Post 4509554)

There is need to know, on which OS you are looking ?
becasue there are many softwares(freeware/Shareware) avalible for the sync. if you have linux you can use "rync" utility.

OS is Linux okusi0 2.6.35-28-server #50-Ubuntu SMP Fri Mar 18 18:59:25 UTC 2011 x86_64 GNU/Linux

i'm afraid rsync of itself is not appropriate for this situation, where you have three active servers that have to update each other, including new files, deleted files, moved files, and modified files.

i need a system like Unison, but which is more stable, less buggy, and maintained.

Quote:

Originally Posted by vasile002 (Post 4509601)

You could try using lsyncd:
http://code.google.com/p/lsyncd/

thanks vasile. yes, i was looking at that very program this morning. but the documentation, such as it is, is not very clear to me. it's also not clear how robust this system would be on often-flakey internet connections here in Indonesia.

does anyone have actual experience using lsyncd to synchronise files on multiple servers as outlined above??

I am using it without problems. It uses rsync to sync the files. You need to set up passwordless rsa key auth between the servers you want synced and you can just run it as one command which makes it run as damoen. See lsyncd --help for all the options

Quote:

Originally Posted by vasile002 (Post 4511113)

thanks vasile. i'm familiar with setting up passwordless rsa keys. i have to do this for Unison and other ssh programs. these are already set up on all my 3 servers.

one of the things that's not clear to me about lsyncd is this: Is it the case that you have to run lsyncd on all servers simultaneously? and is there any sort of special setup required for more than 2 servers?

Yes, it needs to run on all servers and there's nothing special required. Just set it up to sync the locations you need between all 3 servers. For 3 servers I believe you will need to run 2 lsyncd commands on each

Quote:

Originally Posted by vasile002 (Post 4512309)

For 3 servers I believe you will need to run 2 lsyncd commands on each

that sounds like a recipe for a "deadly embrace"! :) anyway, i guess there's nothing for it but to give it a go and see what happens!

Quote:

Originally Posted by kukukachu (Post 4512348)

that sounds like a recipe for a "deadly embrace"! :) anyway, i guess there's nothing for it but to give it a go and see what happens!

right, anyway nothing bad can happen

Quote:

Originally Posted by vasile002 (Post 4513084)

right, anyway nothing bad can happen

hmmmm .... ok. ;)

here's what i've done. keep in mind that i'm still testing, and i'm completely unsure of its robustness.

i have 3 servers. one in Jakarta, one in Bali, and one in Batam. they are all connected to the internet on flaky, consumer-grade 3Mbps connections.

i'm assuming use of an Ubuntu server here; you rpm heads should be smart enough to make the relevant adjustments. ;) also, if you want to use lsyncd -ryncssh, then you will need version 2 or higher, not the 1.x provided on the ubuntu repository. this means getting source code and compiling it yourself. don't panic. this is fairly painless if you have installed all the required dependencies, and this is done within the installation script below.

as root, install the following on each of the servers. (i put this in a file called installlsync.sh.)

Code:

#!/bin/bash



# make sure you have all the files required to compile from source

apt-get -y install build-essential gcc lua5.1 liblua5.1-dev liblua5.1-0 checkinstall



# make sure you have inotify installed.  

apt-get -y install inotify-tools



# this is the standard place for compiling programs from source.

mkdir /usr/local/src/lsyncd

cd /usr/local/src/lsyncd





# download newest lsyncd from lsyncd.googlecode.com (lsyncd-2.0.5.tar.gz)

# you may wish to check for newer versions.  i'm assuming 2.0.5 here.

wget http://lsyncd.googlecode.com/files/lsyncd-2.0.5.tar.gz



# unpack the code

tar xzvf lsyncd-2.0.5.tar.gz



cd lsyncd-2.0.5

./configure

make

make install

checkinstall -y



# note: if you are not using a 64bit server, then deb file 

# below may have a different name

dpkg -i lsyncd_2.0.5-1_amd64.deb



# remember copy the executable to somewhere useful!

cp lsyncd /usr/bin

once successfully installed, you then need to get lsyncd running on all three servers.

the FIRST thing you MUST do is to manually synchronise all the folders on each of the servers. if you don't do this first, you WILL lose files. trust me. i know these things.

so do something like this from your "master" serverJakarta:

Code:

cd /myfolder

rsync -avz . root@serverBali:/myfolder

rsync -avz . root@serverBatam:/myfolder

once everything is 100% in sync, i install this little script on each of the servers to automate/standardise the lsync setup on each machine: (call this script lsyncdgen.sh)

Code:

#!/bin/bash



# get rid of any instances of lsyncd currently running 

# (this assumes there is no activity on your system when you run this!)

killall lsyncd



# nominate a working directory where you are going to put this script 

# and the config file this script generates

wdir=/root/syncfile



# get the hostname of the server this script is running on

thishost=$(cat /etc/hostname)



# now we want to figure out which server we wish to synchronise...

# we have to go around in a circle to avoid deadly embraces ...

if [[ "$thishost" == "serverJakarta" ]]; then

    dst=serverBali

elif [[ "$thishost" == "serverBali" ]]; then

    dst=serverBatam

elif [[ "$thishost" == "serverBatam" ]]; then

    dst=serverJakarta

else

        # you messed up!

        echo "$thishost not on my list!"

        exit 1

fi





# let's make the lua config file for this server ...

echo "-- lsyncd config file for this server ($thishost)" > $wdir/myconfig.lua

# i'm setting up the log files for somewhere where i can find them

echo 'settings = { 

    logfile="/tmp/lsyncd.log", statusFile="/tmp/lsyncd.status", 

}' >> $wdir/myconfig.lua



# these are the rsync options you probably need:

opts="-aluz"



dir=/myfolder/

echo "sync{default.rsyncssh, source=\"$dir\", host=\"$dst\", targetdir=\"$dir\", rsyncOpts=\"$opts\", excludeFrom=\"$wdir/exclude\"}" >> $wdir

echo "" >> $wdir/myconfig.lua



#for each additional folder you want synchronised, do this code: 

#---

dir=/myfolder2/

echo "sync{default.rsyncssh, source=\"$dir\", host=\"$dst\", targetdir=\"$dir\", rsyncOpts=\"$opts\", excludeFrom=\"$wdir/exclude\"}" >> $wdir

echo "" >> $wdir/myconfig.lua

#---





# run lsyncd!

lsyncd  $wdir/myconfig.lua &

now you almost certainly want to exclude certain files from being synchronised. make a file called "exclude" and place in the same directory as the above script:

Code:

*~

~*

.*

that's it. keep an eye on the log files to see what is going on. i've only been using this a few hours, so have not fully tested it. i would be grateful for any input from anyone who has more experience using lsyncd!

NB: remember to ensure that your system can autologin to the destination server using ssh. use this script if this stuff confuses you. press Enter when/if you are presented with a passphrase prompt:

Code:

#!/bin/bash

# sshautologin.sh

if [ -z $1 ]; then

        echo "require destination username and servername"

        exit 1

fi

if [ -z $2 ]; then

        echo "require destination servername"

        exit 1

fi

cd ~

# if you already have a key then don't generate it again

if [ ! -f ~/.ssh/id_dsa.pub ]; then

        # no key! generate one!

        ssh-keygen -t dsa

        chmod 700 ~/.ssh

fi

cat ~/.ssh/id_dsa.pub | ssh -l $1 $2 'cat >> ~/.ssh/authorized_keys'

nice one, thanks for posting detailed steps of how you did it

Lsyncd e-mail & mysql

I have a server (primary) that needs to duplicated for business continuity issues. If I use Lsyncd, can I duplicate users, logins, e-mail and Mysql databases on the Target (secondary) Server, this way if the primary looses the internet, I can change the dns and be up and running? Obviously the e-mail files need to be sync'd with the correct permissions.

IF this is not the product to accomplish this, anyone have any other ideas?

Thanks for the assistance.

Wayne