CentOS 7
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Pen : HTTP Load Balancing
2015/06/10
 
Install pen which is lightweight simple Load Balancing software.
It is TCP protocol based, so it's possible to balance not only HTTP but SMTP, FTP, LDAP and so on.
This example is based on the environment like follows. 
        |
--------+--------------------------------------------------------------------
        |
        +-------------------+--------------------+--------------------+
        |10.0.0.30          |10.0.0.51           |10.0.0.52           |10.0.0.53
 +------+-----+     +-------+------+     +-------+------+     +-------+------+
 |  Frontend  |     |   Backend#1  |     |   Backend#2  |     |   Backend#3  |
 | Pen Server |     |  Web Server  |     |  Web Server  |     |  Web Server  |
 +------------+     +--------------+     +--------------+     +--------------+
 
Configure Pen to load balance to Backend#1, Backend#2, Backend#3 web servers.
[1] Install Pen.
# install from EPEL

[root@dlp ~]#
yum --enablerepo=epel -y install pen
[2] Configure Pen.
[root@dlp ~]#
vi /etc/pen.conf
# create new

# log file

LOGFILE=/var/log/pen.log
# statics report file

WEBFILE=/var/www/pen/webstats.html
# max connections

MAX_CONNECTIONS=256
# send X-Forwarded-For header

XFORWARDEDFOR=true
# Round-Robin mode

ROUNDROBIN=true
# listening port

PORT=80
# number of backends

BACKEND=3
# define backend servers

SERVER1=10.0.0.51:80
SERVER2=10.0.0.52:80
SERVER2=10.0.0.53:80
# create an init script

[root@dlp ~]#
vi /etc/rc.d/init.d/pend 
#!/bin/bash

# pend: Start/Stop Pend
# chkconfig: - 90 10
# description: Pen is a light weight simple load balancer.
# pidfile: /var/run/pen.pid

. /etc/rc.d/init.d/functions
. /etc/pen.conf

LOCKFILE="/var/lock/subsys/pen"
PID=/var/run/pen.pid
PROG=/usr/bin/pen
PROGNAME=Pend

RETVAL=0
start() {
    SERVER=`grep "^SERVER" /etc/pen.conf | cut -d= -f2`
    [ $XFORWARDEDFOR = "true" ] && SERVER="-H $SERVER"
    [ $ROUNDROBIN = "true" ] && SERVER="-r $SERVER"
    [ $SSLCERTS ] && SERVER="-E $SSLCERTS $SERVER"

    echo -n $"Starting $PROGNAME: "
    daemon $PROG $PORT -w $WEBFILE -x $MAX_CONNECTIONS -p $PID -l $LOGFILE -S $BACKEND $SERVER
    RETVAL=$?
    echo
    [ $RETVAL -eq 0 ] && touch $LOCKFILE
    return $RETVAL
}
stop() {
    echo -n $"Stopping $PROGNAME: "
    killproc $PROG
    RETVAL=$?
    echo
    [ $RETVAL -eq 0 ] && rm -f $PID $LOCKFILE
    return $RETVAL
}
case "$1" in
    start)
        start
        ;;
    stop)
        stop
        ;;
    status)
        status -p "$PID" -l $PROG $PROGNAME
        ;;
    restart)
        stop
        start
        ;;
    *)
        echo $"Usage: $0 {start|stop|status|restart}"
        exit 1
esac
exit $?
[root@dlp ~]#
chmod 755 /etc/rc.d/init.d/pend
# create a Systemd setting file

[root@dlp ~]#
vi /usr/lib/systemd/system/pen.service 
[Unit]
Description=Pend service
After=network.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/etc/rc.d/init.d/pend start
ExecStop=/etc/rc.d/init.d/pend stop

[Install]
WantedBy=multi-user.target
[root@dlp ~]#
systemctl start pen

[root@dlp ~]#
systemctl enable pen

[3] Configure httpd on backend servers to record logs of X-Forwarded-For.
[root@www ~]#
vi /etc/httpd/conf/httpd.conf
# line 196: change

LogFormat "
\"%{X-Forwarded-For}i\"
%l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined
[root@www ~]#
systemctl restart httpd

[4] Make sure all works fine to access to the frontend server from a Client with HTTP like follows.
 
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