Here is a set of "actual" scripts, in use at a client for running
a Master/Slave Fail-over pair for a SquidGuard installation. 
The slave kicks in and takes over if the master goes off-line. 
If the master comes back on-line then the slave backs down again.

  http://www.trilug.org/~jonc/Failover_scripts

All these scripts run on the Slave:
  Server_Sync - Keeps the Slave up-to-date with the Master.
                Runs once a night. Note: it expects a nightly
                backup to be run on the Master server. This
                script grabs the first rotated copy of the
                backup tar file, so the slave is always 24 hours
                behind the Master. This is done intentionally 
                so the Slave is always running with a valid 
                and known good configuration.

 Server_check - Runs every minute out of cron to check on 
                the status of the Master server. Initiates
                the Failover or the Return scripts.
 
                The check is three pings in a minute on
                the Primary ethernet card. If all three pings
                fail, then failover is initiated.

                The Master server runs with a public IP address
                and a private IP address. The private IP address
                is an IP alias (eth0:1) running on the same NIC
                as the Public IP. The slave is plugged into
                the same switch (or a parrallel switch) and uses
                an IP alias on the same private network.

 Server_Failover - Script to move the slave onto the network
                as the master, and startup any necessary services

 Server_Return - script to move the slave back off the network
                and into stand-by mode.
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The following files are in /root/config/

   conf_files - The files and directories to be updated nightly
                by Server_Sync (Not a script... just a list).
                Note: be sure to leave the root "/" off of any
                entry - as the backups are stored without the
                root "/" in the tar file.

  network.failover - a copy of the Master's /etc/sysconfig/network file

  ifcfg-eth1.failover - a copy of the Master's
                      /etc/sysconfig/network-scripts/ifcfg-eth1 file

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The directory /root/master_backup/  is also used as a storage place for
the most recent system backup of the Master server.