Add Memory to Running Linux system

Hello guys,
As we know Linux is open source and highly customization can we think of adding Memory to linux system on the fly.Yes it possible.as we can add a swap memory to Running Linux system on the fly.

So the next question is how can we do it....?
It can be done as follows...

I need additional swap space to improve my Linux server/desktop system performance. How do I add a swap file to Linux system using command line options without creating a new partitions?

In Linux, as in most other Unix-like operating systems, it is common to use a whole partition of a hard disk for swapping. However, with the 2.6 Linux kernel, swap files are just as fast as swap partitions, although I recommends using a swap partition. The administrative flexibility of swap files outweighs that of partitions; since modern high capacity hard drives can remap physical sectors, no partition is guaranteed to be contiguous. You can add swap file as a dedicated partition or use following instructions to create a swap file.

Procedure To Add a Swap File Under Linux

You need to use the dd command to create swap file. The mkswap command is used to set up a Linux swap area on a device or in a file.

Step #1: Login as the Root User

Open a terminal window (select Applications > Accessories > Terminal) or login to remote server using the ssh client. Switch to the root user by typing su - (or sudo -s) and entering the root password, when prompted:
$ su -
OR
$ sudo -s

Step #2: Create Storage File

Type the following command to create 512MB swap file (1024 * 512MB = 524288 block size):
# dd if=/dev/zero of=/swapfile1 bs=1024 count=524288
Sample outputs:

524288+0 records in
524288+0 records out
536870912 bytes (537 MB) copied, 3.23347 s, 166 MB/s

Where,

1. if=/dev/zero : Read from /dev/zero file. /dev/zero is a special file in that provides as many null characters to build storage file called /swapfile1.
2. of=/swapfile1 : Read from /dev/zero write storage file to /swapfile1.
3. bs=1024 : Read and write 1024 BYTES bytes at a time.
4. count=524288 : Copy only 523288 BLOCKS input blocks.

Step #3: Set Up a Linux Swap Area

Type the following command to set up a Linux swap area in a file:
# mkswap /swapfile1
Sample outputs:

Setting up swapspace version 1, size = 524284 KiB
no label, UUID=e1fe2038-6554-4d1a-a108-037acd4e02e2

Setup correct file permission for security reasons, enter:
# chown root:root /swapfile1
# chmod 0600 /swapfile1
A world-readable swap file is a huge local vulnerability. The above command make sure only root user can read/write to the file. Finally, activate /swapfile1 swap space immediately, enter:
# swapon /swapfile1

Update /etc/fstab file

To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab file. Open this file using a text editor such as vi:
# vi /etc/fstab
Append the following line:
/swapfile1 swap swap defaults 0 0
Save and close the file. Next time Linux comes up after reboot, it enables the new swap file for you automatically.

How do I Verify Swap is Activated or Not?

Simply use the free command:
$ free -m

             total       used       free     shared    buffers     cached
Mem:          1876       1798         77          0        119       1440
-/+ buffers/cache:        237       1638
Swap:         4607          0       4607

How can I display swap usage summary on Linux?

Type the following swapon command:
# swapon -s
Sample outputs:

Filename    Type  Size Used Priority
/dev/sda6                               partition 4194296 0 0
/swapfile1                              file  524280 0 -1

Another option is to view /proc/meminfo file:
$ less /proc/meminfo
$ grep -i --color swap /proc/meminfo
Sample outputs:

SwapCached:        30748 kB
SwapTotal:       6291448 kB
SwapFree:        6154008 kB

You can also use top command, atop command, and/or htop command to display information about swap usage:
# top
# atop
# htop
Sample outputs from a database server running on a CentOS Linux server:

  1  [||                        3.9%]     Tasks: 171, 106 thr; 1 running
  2  [                          0.0%]     Load average: 0.06 0.12 0.09
  3  [||                        2.0%]     Uptime: 22 days, 07:07:28
  4  [                          0.0%]
  5  [                          0.0%]
  6  [                          0.0%]
  7  [                          0.0%]
  8  [                          0.0%]
  Mem[||||||||||||||||||2112/11909MB]
  Swp[|                   134/6143MB]
  PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
 8523 mysql      20   0 4545M  414M  4816 S  0.0  3.5  0:00.00 /usr/libexec/mysq
 8524 mysql      20   0 4545M  414M  4816 S  0.0  3.5  0:02.74 /usr/libexec/mysq
 8525 mysql      20   0 4545M  414M  4816 S  0.0  3.5  0:16.17 /usr/libexec/mysq
 8526 mysql      20   0 4545M  414M  4816 S  0.0  3.5  0:06.33 /usr/libexec/mysq
 8528 mysql      20   0 4545M  414M  4816 S  0.0  3.5  4:02.14 /usr/libexec/mysq
 8529 mysql      20   0 4545M  414M  4816 S  0.0  3.5  5:22.00 /usr/libexec/mysq
 8530 mysql      20   0 4545M  414M  4816 S  0.0  3.5  0:04.63 /usr/libexec/mysq
 8531 mysql      20   0 4545M  414M  4816 S  0.0  3.5  0:50.95 /usr/libexec/mysq
 8532 mysql      20   0 4545M  414M  4816 S  0.0  3.5  0:08.10 /usr/libexec/mysq
 9359 mysql      20   0 4545M  414M  4816 S  0.0  3.5 22:53.28 /usr/libexec/mysq

How can I disable devices and files for paging and swapping on Linux?

You need to use the swapoff command:
# swapoff /swapfile1
# swapon -s

How do I set swappiness on a Linux server?

The syntax is:
# sysctl vm.swappiness=VALUE
# sysctl vm.swappiness=20
OR
# echo VALUE > /proc/sys/vm/swappiness
# echo 30 > /proc/sys/vm/swappiness
The value in /proc/sys/vm/swappiness file controls how aggressively the kernel will swap memory pages. Higher values increase agressiveness, lower values descrease aggressiveness. The default value is 60. To make changes permanent add the following line to/etc/sysctl.conf:

 
echo 'vm.swappiness=30' >> /etc/sysctl.conf
 

and we are done guys..

Install OpenERP From Source

Hello Guys,

Welcome Back on my blog Today I will tell you about install OpenERP  from source as its most recommended   for production environment as an administrator we must know it.As This is the most stable way to install OpenERP.

Step 1. Build your server
I install just the bare minimum from the install routine (you may want to install the openssh-server during the install procedure or install subsequently depending on your needs).

After the server has restarted for the first time I install the openssh-server package (so we can connect to it remotely) and denyhosts to add a degree of brute-force attack protection. There are other protection applications available: I’m not saying this one is the best, but it’s one that works and is easy to configure and manage. If you don’t already, it’s also worth looking at setting up key-based ssh access, rather than relying on passwords. This can also help to limit the potential of brute-force attacks.
[NB: This isn't a How To on securing your server...]

#sudo apt-get install openssh-server denyhosts

Now make sure your server has all the latest versions & patches by doing an update:

#sudo apt-get update
#sudo apt-get dist-upgrade

Although not always essential it’s probably a good idea to reboot your server now and make sure it all comes back up and you can login via ssh.

Now we’re ready to start the OpenERP install.

Step 2. Create the OpenERP user that will own and run the application

#sudo adduser --system --home=/opt/openerp --group openerp -s /bin/bash

This is a “system” user. It is there to own and run the application, it isn’t supposed to be a person type user with a login etc. In Ubuntu, a system user gets a UID below 1000, has no shell (it’s actually /bin/false) and has logins disabled. Note that I’ve specified a “home” of /opt/openerp, this is where the OpenERP server code will reside and is created automatically by the command above. The location of the server code is your choice of course, but be aware that some of the instructions and configuration files below may need to be altered if you decide to install to a different location.

[Note: If you want to run multiple versions of OpenERP on the same server, the way I do it is to create multiple users with the correct version number as part of the name, e.g. openerp70, openerp61 etc. If you also use this when creating the Postgres users too, you can have full separation of systems on the same server. I also use similarly named home directories, e.g. /opt/openerp70, /opt/openerp61 and config and start-up/shutdown files. You will also need to configure different ports for each instance or else only the first will start.]

This will su your current terminal login to the openerp user (the “-” between su and openerp is correct) and use the shell /bin/bash. When this command is run you will be in openerp’s home directory: /opt/openerp.

When you have done what you need you can leave the openerp user’s shell by typing exit.

Step 3. Install and configure the database server, PostgreSQL

#sudo apt-get install postgresql

Then configure the OpenERP user on postgres:

First change to the postgres user so we have the necessary privileges to configure the database.

#sudo su - postgres

Now create a new database user. This is so OpenERP has access rights to connect to PostgreSQL and to create and drop databases. Remember what your choice of password is here; you will need it later on:

#createuser --createdb --username postgres --no-createrole --no-superuser --pwprompt openerp

Finally exit from the postgres user account:

exit

Step 4. Install the necessary Python libraries for the server

#sudo apt-get install python-dateutil python-docutils python-feedparser python-gdata \
python-jinja2 python-ldap python-libxslt1 python-lxml python-mako python-mock python-openid \
python-psycopg2 python-psutil python-pybabel python-pychart python-pydot python-pyparsing \
python-reportlab python-simplejson python-tz python-unittest2 python-vatnumber python-vobject \
python-webdav python-werkzeug python-xlwt python-yaml python-zsi

With that done, all the dependencies for installing OpenERP 7.0 are now satisfied (note that there are some new packages required since 6.1).

Step 5. Install the OpenERP server
I tend to use wget for this sort of thing and I download the files to my home directory.

Make sure you get the latest version of the application: at the time of writing this it’s 7.0. I got the download links from their download pages (note there are also deb, rpm and exe builds in this area too). There isn’t a static 7.0 release tarball as such anymore, but there is a nightly build of the 7.0 source tree which should be just as good and will contain patches as and when things get fixed. The link below is to the source tarball for the 7.0 branch.

Note: As an alternative method of getting the code onto your server, Jerome added a very useful comment showing how to get it straight from launchpad. Thanks!

#wget http://nightly.openerp.com/7.0/nightly/src/openerp-7.0-latest.tar.gz

Now install the code where we need it: cd to the /opt/openerp/ directory and extract the tarball there.

#cd /opt/openerp
#sudo tar xvf ~/openerp-7.0-latest.tar.gz

Next we need to change the ownership of all the the files to the OpenERP user and group we created earlier.

#sudo chown -R openerp: openerp

And finally, the way I have done this is to copy the server directory to something with a simpler name so that the configuration files and boot scripts don’t need constant editing (I called it, rather unimaginatively, server). I started out using a symlink solution, but I found that when it comes to upgrading, it seems to make more sense to me to just keep a copy of the files in place and then overwrite them with the new code. This way you keep any custom or user-installed modules and reports etc. all in the right place.

#sudo cp -a openerp-7.0 server

As an example, should OpenERP 7.0.1 come out soon, I can extract the tarballs into /opt/openerp/ as above. I can do any testing I need, then repeat the copy command so that the modified files will overwrite as needed and any custom modules, report templates and such will be retained. Once satisfied the upgrade is stable, the older 7.0 directories can be removed if wanted.

That’s the OpenERP server software installed. The last steps to a working system is to set up the configuration file and associated boot script so OpenERP starts and stops automatically when the server itself stops and starts.

Step 6. Configuring the OpenERP application
The default configuration file for the server (in /opt/openerp/server/install/) is actually very minimal and will, with only one small change work fine so we’ll simply copy that file to where we need it and change it’s ownership and permissions:

#sudo cp /opt/openerp/server/install/openerp-server.conf /etc/
#sudo chown openerp: /etc/openerp-server.conf
#sudo chmod 640 /etc/openerp-server.conf

The above commands make the file owned and writeable only by the openerp user and group and only readable by openerp and root.

To allow the OpenERP server to run initially, you should only need to change one line in this file. Toward to the top of the file change the line db_password = False to the same password you used back in step 3. Use your favourite text editor here. I tend to use nano, e.g.

#sudo vim /etc/openerp-server.conf

One other line we might as well add to the configuration file now, is to tell OpenERP where to write its log file. To complement my suggested location below add the following line to the openerp-server.conf file:

#logfile = /var/log/openerp/openerp-server.log

Once the configuration file is edited and saved, you can start the server just to check if it actually runs.

#sudo su - openerp -s /bin/bash 
#/opt/openerp/server/openerp-server

If you end up with a few lines eventually saying OpenERP is running and waiting for connections then you are all set.

The Ubuntu 12.04 packaged version of the python gdata client library is not quite recent enough, so to install a more up-to-date version I did the following (exit from the openerp user’s shell if you are still in it first):

#sudo apt-get install python-pip
#sudo pip install gdata --upgrade

Going back and repeating the commands to start the server resulted in no further warnings

#sudo su - openerp -s /bin/bash
#/opt/openerp/server/openerp-server

If there are errors, you’ll need to go back and find out where the problem is.

Otherwise simply enter CTL+C to stop the server and then exit to leave the openerp user account and go back to your own shell.

Step 7. Installing the boot script
For the final step we need to install a script which will be used to start-up and shut down the server automatically and also run the application as the correct user. There is a script you can use in /opt/openerp/server/install/openerp-server.init but this will need a few small modifications to work with the system installed the way I have described above. Here’s a link to the one I’ve already modified for 7.0.

Similar to the configuration file, you need to either copy it or paste the contents of this script to a file in /etc/init.d/ and call it openerp-server. Once it is in the right place you will need to make it executable and owned by root:

#sudo chmod 755 /etc/init.d/openerp-server
#sudo chown root: /etc/init.d/openerp-server

In the configuration file there’s an entry for the server’s log file. We need to create that directory first so that the server has somewhere to log to and also we must make it writeable by the openerp user:

#sudo mkdir /var/log/openerp
#sudo chown openerp:root /var/log/openerp

Step 8. Testing the server
To start the OpenERP server type:

#sudo /etc/init.d/openerp start

You should now be able to view the logfile and see that the server has started.

#less /var/log/openerp/openerp-server.log

If there are any problems starting the server you need to go back and check. There’s really no point ploughing on if the server doesn’t start…

Here is the file which you need to copy paste in /etc/init.d/openerp

#!/bin/sh

### BEGIN INIT INFO
# Provides:             openerp-server
# Required-Start:       $remote_fs $syslog
# Required-Stop:        $remote_fs $syslog
# Should-Start:         $network
# Should-Stop:          $network
# Default-Start:        2 3 4 5
# Default-Stop:         0 1 6
# Short-Description:    Enterprise Resource Management software
# Description:          Open ERP is a complete ERP and CRM software.
### END INIT INFO

PATH=/bin:/sbin:/usr/bin
DAEMON=/opt/openerp/server/openerp-server
NAME=openerp-server
DESC=openerp-server

# Specify the user name (Default: openerp).
USER=openerp

# Specify an alternate config file (Default: /etc/openerp-server.conf).
CONFIGFILE="/etc/openerp-server.conf"

# pidfile
PIDFILE=/var/run/$NAME.pid

# Additional options that are passed to the Daemon.
DAEMON_OPTS="-c $CONFIGFILE"

[ -x $DAEMON ] || exit 0
[ -f $CONFIGFILE ] || exit 0

checkpid() {
    [ -f $PIDFILE ] || return 1
    pid=`cat $PIDFILE`
    [ -d /proc/$pid ] && return 0
    return 1
}

case "${1}" in
        start)
                echo -n "Starting ${DESC}: "

                start-stop-daemon --start --quiet --pidfile ${PIDFILE} \
                        --chuid ${USER} --background --make-pidfile \
                        --exec ${DAEMON} -- ${DAEMON_OPTS}

                echo "${NAME}."
                ;;

        stop)
                echo -n "Stopping ${DESC}: "

                start-stop-daemon --stop --quiet --pidfile ${PIDFILE} \
                        --oknodo

                echo "${NAME}."
                ;;

        restart|force-reload)
                echo -n "Restarting ${DESC}: "

                start-stop-daemon --stop --quiet --pidfile ${PIDFILE} \
                        --oknodo
      
                sleep 1

                start-stop-daemon --start --quiet --pidfile ${PIDFILE} \
                        --chuid ${USER} --background --make-pidfile \
                        --exec ${DAEMON} -- ${DAEMON_OPTS}

                echo "${NAME}."
                ;;

        *)
                N=/etc/init.d/${NAME}
                echo "Usage: ${NAME} {start|stop|restart|force-reload}" >&2
                exit 1
                ;;
esac

exit 

#--------------------------------------------------------------

Enjoy.................

If you want a shell script so let me know ..

Install Syslog Server (Syslog-ng) on CentOS

Syslog-NG and CentOS 6.x

Requirements:

• CentOS 6.x (or other Redhat based flavor)
• Internet Connectivity
• chkconfig (yum install chkconfig)
• wget (yum install wget)

Installation:

Install the prerequisite first.

 # yum install chkconfig wget

Install EPEL Repositories:

1. Login to your server as root (or su root)
2. Type: cd /root
3. Type (Current link as of this post):

#wget http://dl.fedoraproject.org/pub/epel/6Server/i386/epel-release-6-8.noarch.rpm

 #rpm -Uvh /root/epel-release-6-8.noarch.rpm

#yum repolist

Install Syslog-NG:

 Run update check:

 #yum check-update

To see if this will impact any other software on your system.

Check the availability of Syslog-NG by typing:

# yum list *syslog-ng*

Configure CentOS Services, Stop Rsyslog, and Start Syslog-NG:

Disable rsyslog: 

#chkconfig rsyslog off

Confirm rsyslog is disabled:

#chkconfig syslog-ng on

service rsyslog stop

service syslog-ng start

1. Example Configuration for Syslog-NG:
1. Add the following to the END of /etc/syslog-ng/syslog-ng.conf:

   # My Switches
   source s_navneet { 
           udp(ip(0.0.0.0) port(514));
           tcp(ip(0.0.0.0) port(514)); 
   };
   
   destination d_navneet {
           file(
                   "/var/log/navneet/$HOST-$YEAR$MONTH$DAY.log"
                   perm(644)
                   create_dirs(yes)
           );
   };
   
    
   log { source(s_navneet); destination(d_navneet); };

   This will basically take ALL (udp/tcp 0.0.0.0) syslog data and place it into /var/log/navneet. The names of the files are based off the host name and date. For example, if you have switch named MYSWITCH and the current date is May 8th, 2014… the full path and file name would be: /var/log/navneet/nrathi-VBox-20140508.log
2. *** DO NOT modify any other portion of the file unless you are certain you know what you are doing!
3. Restart the syslog-ng service to implement changes:

   [root@myserver syslog-ng]# service syslog-ng restart
   Stopping syslog-ng:                                        [  OK  ]
   Starting syslog-ng:                                        [  OK  ]

4. Delete Old Syslog-NG Files:

5. Login as root Type:  

6. crontab -e

7. Add the following to your crontab file:

# Delete Old Syslog Files
# 3 AM, Every Sunday
0 3 * * 0 /usr/bin/find /var/log/cisco -maxdepth 1 -mtime 90 -name *.log -exec rm {} \;

Change the "90" to your desired number of days.

ClamAV Installation and Scanning on CentOS

  ClamAV open source antivirus engine

ClamAV is an open source (GPL) antivirus engine designed for detecting Trojans, viruses, malware and other malicious threats. It is the de facto standard for mail gateway scanning. It provides a high performance mutli-threaded scanning daemon, command line utilities for on demand file scanning, and an intelligent tool for automatic signature updates

CentOS 6 – 32-bit

rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

 CentOS 6 – 64-bit

rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

 CentOS 5 – 32-bit

rpm -Uvh http://dl.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm

 CentOS 5 – 64-bit

rpm -Uvh http://dl.fedoraproject.org/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm

After running the above commands for your relevant CentOS version, the following file is created:

/etc/yum.repos.d/epel.repo

The above file can be edited directly to enable or disable the EPEL repo.

2. Install required ClamAV packages

yum install clamav clamd

3. Start the clamd service and set it to auto-start

/etc/init.d/clamd on
chkconfig clamd on
/etc/init.d/clamd start

4. Update ClamAV’s signatures

/usr/bin/freshclam

Note: ClamAV will update automatically, as part of /etc/cron.daily/freshclam.

B. Configure Daily Scan

In this example, we will configure a cronjob to scan the /home/ directory every day:

1. Create cron file:

vim /etc/cron.daily/manual_clamscan

Add the following to the file above. Be sure to change SCAN_DIR to the directory that you want to scan:

#!/bin/bash
SCAN_DIR="/home"
LOG_FILE="/var/log/clamav/manual_clamscan.log"
/usr/bin/clamscan -i -r $SCAN_DIR >> $LOG_FILE

Give our cron script executable permissions:

chmod +x /etc/cron.daily/manual_clamscan

You can even run the above script to ensure that it works correctly.

And you’re done! That should be the minimum required to

 00 10 * * * * root freshclam 

This command will update ClamAV database at 10 am every day.

Good Luck ....!!!

Install Mysql 5.5 from source on Centos

To install MySQL from source you need to install some dependencies and tools co compile from source

MySQL released 5.5 version in December 2010. This version seems to be more efficient with improvements like better improved scalability on multi-core CPU, InnoDB storage engine becomes the default engine for new tables or integration of semisynchronous replication. This version is recommended for production environments. It's interesting for administrator to thinking about upgrading. Much systems executes 5.1 version and sometimes the upgrade can be scary ... Here we are going to see how to install 5.5 version on new systems. First we need to install some packages that are needed by MySQL. So installs (or be sure that they all have been installed): bison, bzr, cmake, gcc-c++ ncurses-devel.

# yum groupinstall 'Development Tools'

# yum install -y bison bzr cmake gcc-c++ ncurses-devel

Then add new mysql account and group: 

# groupadd mysql

# useradd -r -g mysql mysql

Now we need download last mysql 5.5 tar.gz archive, choose the mirror directly on mysql website. 

wget http://URL_OF_MIRROR/mysql-5.5.16.tar.gz

Extracting tar.gz archive 

tar -xvzf /downloads/mysql-5.5.16.tar.gz

Now go into extracted directory and execute cmake: 

cd /downloads/mysql-5.5.16/

cmake . -DCMAKE_INSTALL_PREFIX=/opt/mysql \-DMYSQL_DATADIR=/var/lib/mysql \

-DSYSCONFDIR=/etc \

-DINSTALL_PLUGINDIR=/opt/mysql/lib/mysql/plugin

Note that I use /opt/mysql for basedir /var/lib/mysql for datadir, you can use others directories by specifing them with 'DCMAKE_INSTALL_PREFIX' and '-DMYSQL_DATADIR' options. When cmake finish to work, we can launch the make . 

make

Next, if we don't encounter errors, we launch the install: 

make install

Now, we create symbolic links to have mysql commands in shell: 

ln -s /opt/mysql/bin/* /usr/bin/

Assign owner and group:

 

cd /opt/mysql/

chgrp -R mysql .

chown -R root .

chown -R mysql data

Default database installation: 

scripts/mysql_install_db --user=mysql --datadir=/var/lib/mysql/

Copy a mysql default configuration file: 

cp support-files/my-medium.cnf /etc/my.cnf

Copy mysql init.d script and make it executable: 

cp support-files/mysql.server /etc/init.d/mysqld

chmod 755 /etc/init.d/mysqld

Now edit this init.d script for customize both basedir and datadir paths: 

vim /etc/init.d/mysqld

## replace

basedir=

basedir=

## by

basedir=/opt/mysql

datadir=/var/lib/mysql

Finally, we can launch mysql server and begin to use it: 

/etc/init.d/mysqld start

and we are done

Install HAproxy for high performance and HA

Install HA-proxy as load balance in webserver

Hello Guys, 

Welcome back again on my rathinavneet.blogspot.in.

 I will tell you how you can setup your HA proxy in 10 min for high availability from source so that if one of your web server down it wont affect you much.as your other server are working just fine and your company's or clients business is uninterrupted.

          HA  proxy work on transport layer protocol so same proxy can be use for multiple application.

It will server a great like same ha proxy can be used to configure the Mysql server as well as apache web-server or nginx or tomcat and many more.You will also get the statistics of the network in real time look at the image below.

 Look in the image you can see that  its showing the working web-server by green.Stop or not working or not responding web server by red.

Its working as proxy server as well as a load balance.

Lets start with installation and configuration.I am using ubuntu 12.04 as my host machine.

so 

apt-get install haproxy

This will do the trick and install haproxy fro me.

 We also need to enable the ha proxy in init script so edit the following file 

nano /etc/default.haproxy

 enable = 1

 

Then start with the configuration first of all backup your existing haproxy.conf file to haproxy.back file

mv /etc/haproxy/haproxy.cfg /etc/haproxy/haproxy.cfg.back

global
        log 127.0.0.1   local0
        log 127.0.0.1   local1 notice
        maxconn 4096
        user haproxy
        group haproxy

The log directive mentions a syslog server to which log messages will be sent. On Ubuntu rsyslog is already installed and running but it doesn't listen on any IP address. We'll modify the config files of rsyslog later.
The maxconn directive specifies the number of concurrent connections on the frontend. The default value is 2000 and should be tuned according to your VPS' configuration.
The user and group directives changes the HAProxy process to the specified user/group. These shouldn't be changed.

defaults
    log     global
    mode    http
    option  httplog
    option  dontlognull
    retries 3
    option redispatch

    maxconn 4096 

    timeout connect  5000
    timeout client  50000
    timeout server  50000

We're specifying default values in this section. The values to be modified are the various timeout directives. The connect option specifies the maximum time to wait for a connection attempt to a VPS to succeed.
The client and server timeouts apply when the client or server is expected to acknowledge or send data during the TCP process. HAProxy recommends setting the client and server timeouts to the same value.
The retries directive sets the number of retries to perform on a VPS after a connection failure.
The option redispatch enables session redistribution in case of connection failures. So session stickness is overriden if a VPS goes down.

On Web-server 1 & 2
Create a file in web-servers called check.txt using command  and we will configure the same in ha proxy to check for the particular file if file found when server is ping that means server is operational.
for HA-proxy and proxy will show it as green in the panel.

listen ApplicationCluster 192.168.1.100:80
       mode http
       stats enable
       stats auth nrathi:nrathi123
       balance roundrobin
       cookie JSESSIONID prefix
       option httpclose
       option forwardfor
       option httpchk HEAD /check.txt HTTP/1.0

       server webserver1 192.168.1.102:80 cookie A check
       server webserver2 192.168.1.103:80 cookie B check

This contains configuration for both the frontend and backend. We are configuring HAProxy to listen on port 80 for appname which is just a name for identifying an application. The stats directives enable the connection statistics page and protects it with HTTP Basic authentication using the credentials specified by the stats auth directive.
This page can viewed with the URL mentioned in stats uri so in this case, it is http://192.168.1.100/haproxy?stats

a demo of this page can be viewed here.

The balance directive specifies the load balancing algorithm to use. Options available are Round Robin (roundrobin), Static Round Robin (static-rr), Least Connections (leastconn), Source (source), URI (uri) and URL parameter (url_param).
Information about each algorithm can be obtained from the official documentation.
The server directive declares a backend server, the syntax is:
server <name> <address>[:port] [param*] 

  The name we mention here will appear in logs and alerts. There are many paratmeters supported by this directive and we'll be using the check and cookie parameters in this article. The check option enables health checks on the VPS otherwise, the VPS is
always considered available.
Once you're done configuring start the HAProxy service:
 
sudo service haproxy start

SO the sample configuration file is as follows:

global
        log 127.0.0.1   local0
        log 127.0.0.1   local1 notice
        #log loghost    local0 info
        maxconn 4096
        #debug
        #quiet
        user haproxy
        group haproxy

defaults
    log     global
    mode    http
    option  httplog
    option  dontlognull
    retries 3

    option redispatch

    maxconn 4096 

    timeout connect  5000
    timeout client  50000
    timeout server  50000

 

listen webfarm 192.168.1.100:80
       mode http
       stats enable
       stats auth someuser:somepassword
       balance roundrobin
       cookie JSESSIONID prefix
       option httpclose
       option forwardfor
       option httpchk HEAD /check.txt HTTP/1.0
       server webA 192.168.1.102:80 cookie A check
       server webB 192.168.1.103:80 cookie B check 

# and thats it we are ready to go.