LOAD BALANCE WEB SERVER USE PEN

I/Intro

This is pen, a load balancer for "simple" tcp based protocols such as http or smtp. It allows several servers to appear as one to the outside and automatically detects servers that are down and distributes clients among the available servers. This gives high availability and scalable performance.

The load balancing algorithm keeps track of clients and will try to send them back to the server they visited the last time. The client table has a number of slots (default 2048, settable through command-line arguments). When the table is full, the least recently used one will be thrown out to make room for the new one.

This is superior to a simple round-robin algorithm, which sends a client that connects repeatedly to different servers. Doing so breaks applications that maintain state between connections in the server, including most modern web applications.

When pen detects that a server is unavailable, it scans for another starting with the server after the most recently used one. That way we get load balancing and "fair" failover for free.

Correctly configured, pen can ensure that a server farm is always available, even when individual servers are brought down for maintenance or reconfiguration. The final single point of failure, pen itself, can be eliminated by running pen on several servers, using vrrp to decide which is active.

Refer:

http://siag.nu/pen/

II/Install

This example is based on follwing environmet.

(1) cluster.test.vn [192.168.20.101] Pen Server
(2) www1.test.vn [192.168.20.203] Web Server #1
(3) www2.test.vn [192.168.20.83] Web Server #2

1/Install and configure Pen
[root@ ~]# wget http://dag.wieers.com/rpm/packages/pen/pen-0.17.2-1.el5.rf.i386.rpm
[root@ ~]#rpm -Uvh pen-0.17.2-1.el5.rf.i386.rpm
[root@ ~]#vim /etc/rc.d/init.d/pen

# make scripts

# an example

#!/bin/bash
#
# Pen: Starting Pen
#
# chkconfig: 345 93 92
# description:Simple load-balancer
# processname: pen

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

pen="/usr/local/bin/pen"
lockfile="/var/lock/subsys/pen"
prog="pen"
RETVAL=0

# PID file

PID=/var/run/pen.pid-80

# log file

LOGFILE=/var/log/pen.log

# control port

CONTROL=localhost:10080

# max connections

MAX_CONNECTIONS=500

# port

PORT=80

# number of servers

SERVERS=2

# IP of a server #1

SERVER1=192.168.20.203:80

# IP of a server #2

SERVER2=192.168.20.83:80

start() {
echo -n $"Starting $prog: "
daemon $pen -x $MAX_CONNECTIONS -S $SERVERS -p $PID -l $LOGFILE -C $CONTROL -r $PORT $SERVER1 $SERVER2
RETVAL=$?
echo
[ $RETVAL = 0 ] && touch $lockfile
return $RETVAL
}
stop() {
echo -n $"Stopping $prog: "
killproc $pen
RETVAL=$?
echo
[ $RETVAL = 0 ] && rm -f $lockfile
return $RETVAL
}
case "$1" in
start)
start
;;
stop)
stop
;;
restart)
stop
start
;;
status)
status $pen
;;
*)
echo "Usage: $prog {start|stop|restart|status}"
exit 1
esac

exit $?

[root@lan ~]#vi /etc/logrotate.d/pen

# an example

/var/log/pen.log { daily copytruncate compress notifempty missingok postrotate /etc/rc.d/init.d/pen restart 2>&1 > /dev/null || true endscript }

[root@lan ~]#chmod 755 /etc/rc.d/init.d/pen
[root@lan ~]#/etc/rc.d/init.d/pen startStarting pen: [ OK ]
[root@lan ~]#chkconfig --add pen
[root@lan ~]#chkconfig pen on

2/Configure a tool that shows status of Pen from web browser.

[root@lan ~]#vi /etc/rc.d/init.d/pen

# line 16: specify html file

WEBFILE=/var/www/html/pen/index.html

PID=/var/run/pen.pid-80 LOGFILE=/var/log/pen.log

# add options

daemon $pen -w $WEBFILE -x $MAX_CONNECTIONS -S $SERVERS -p $PID -l $LOGFILE -C $CONTROL -r $PORT $SERVER1 $SERVER2

[root@lan ~]#cp /usr/local/doc/pen/penstats /usr/local/bin/
[root@lan ~]#vi /usr/local/bin/penstats
#!/bin/sh PENHOME=/home/ulric/Projekt/pen PIDFILE=/var/run/pen.pid-80

# change

WEBFILE=/var/www/html/pen/index.html

# change

# This will make pen save its stats kill -USR1 `cat $PIDFILE` # We don't know how long it will take; wait a few seconds sleep 2 # And display the results echo "Content-type: text/html" echo cat $WEBFILE

[root@lan ~]#/etc/rc.d/init.d/pen restart
Stopping pen:[ OK ]
Starting pen:[ OK ]
[root@lan ~]#chmod 755 /usr/local/bin/penstats
[root@lan ~]#/usr/local/bin/penstats# run
[root@lan ~]#crontab -e

*/1 * * * * /usr/local/bin/penstats

3/Access to Pen server with web browser. A backend server answers normally like below.

a/First Request


b/Second request


4/ Stop httpd on a server now and access to pen server again. Another backend server answers normally like below.

a/ Stop http in 192.168.20.203



b/ Stop http in 192.168.20.83

Note:you need configure Apache listen port 81:

change listen port 80 to 81
Besides Pen can loadbalance other service (FTP,HTTPS,SMTP,POP3...)

pen -l pen443.log -p pen443.pid 192.168.20.101:443
192.168.20.203:443 192.168.20.83:443
(LOAD BALANCE HHTPS)

pen -l pen110.log -p pen110.pid 192.168.20.101:110
192.168.20.203:110 192.168.20.83:110
(LOAD BALANCE POP3)

pen -l pen25.log -p pen25.pid 192.168.20.101:25
192.168.20.203:25 192.168.20.83:25
(LOAD BALANCE SMTP)

pen -l pen21.log -p pen21.pid 192.168.20.101:21
192.168.20.203:21 192.168.20.83:21
(LOAD BALANCE FTP)