IP Address Overtaking

[Dejvid Zaninovic]

I could not find any non-commercial IP Address overtaking solution for
FreeBSD so I wrote this simple shell script.  If you find it useful you can
use it.

-----------
#!/usr/local/bin/ksh
#
# Node v0.01
#
#     purpose:
#         - very simple ip address overtaking for FreeBSD systems
#         - can be used as simple apache clustering solution if used
#           with mod_backhand
#
#     tested to work on:
#         - FreeBSD v4.1.1
#         - pdksh v5.2.14
#         - fping v2.2b1
#
#     command line arguments:
#         - node_name: resolvable name of the virtual node
#
#     instructions:
#         - configure config section in the script
#         - run the same scipt on two or more cluster nodes using nohup
#         - for more virtual nodes run same script many times
#
#     signals:
#         - send INT or TERM signal to stop the virtual node
#         - send HUP signal to switch virtual node to another node,
#           if another node don't take over the virtual node in 5 seconds
#           virtual node is switched back
#
# versions:
#
# v0.01 - 01.19.2001 - Dejvid Zaninovic ([EMAIL PROTECTED])
#     - initial version
#

# config section

NETWORK_INTERFACE=xl0
TMPDIR=/tmp


# command line arguments

SCRIPT_NAME=$0
NODE_ADDRESS=$1


# global vars init

NODE_ETHER=$(ifconfig $NETWORK_INTERFACE | grep ether | cut -d" " -f2)
LOCKFILE=$TMPDIR/$SCRIPT_NAME.$NODE_ADDRESS.lock
MASTER=false


# functions

usage()
{
    print -u2 "usage: $SCRIPT_NAME node_name"
    exit 1
}


node_up()
{
    print $SCRIPT_NAME: $NODE_ADDRESS: up
    ifconfig $NETWORK_INTERFACE alias $NODE_ADDRESS netmask 0xffffffff
    arp -S $NODE_ADDRESS $NODE_ETHER pub > /dev/null 2>&1
}


node_down()
{
    if $MASTER
    then
        print $SCRIPT_NAME: $NODE_ADDRESS: down
        ifconfig $NETWORK_INTERFACE -alias $NODE_ADDRESS netmask 0xffffffff
        arp -d $NODE_ADDRESS > /dev/null 2>&1
        route delete $NODE_ADDRESS > /dev/null 2>&1
    fi
}


node_check()
{
    fping -q $NODE_ADDRESS
}


node_kill()
{
    node_down
    rm $LOCKFILE
    print $SCRIPT_NAME: $NODE_ADDRESS: exit
    exit 0
}


node_switch()
{
    print $SCRIPT_NAME: $NODE_ADDRESS: switch
    node_down
    sleep 5
}


# main

trap node_kill INT TERM
trap node_switch HUP

if [[ $# -ne 1 ]]
then
    usage
fi

if [[ -f $LOCKFILE ]]
then
    print -u2 "$SCRIPT_NAME: $NODE_ADDRESS node is already running"
    exit 1
fi

touch $LOCKFILE

print $SCRIPT_NAME: $NODE_ADDRESS: started

while true
do
    node_check

    if [[ $? -ne 0 ]]
    then
        MASTER=true
        node_up
    fi

    sleep 1
done




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