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Chapter 14 Working with Network Services 247
Configuring IP Failover
You configure failover behavior using scripts. The scripts must be executable (for
example, shell scripts, Perl, compiled C code, or executable AppleScripts). You place
these scripts in /Library/IPFailover/IP_address on the secondary server.
You need to create a folder named with the public IP address of the primary server to
contain the failover scripts for that server. For example, /Library/IPFailover/100.0.0.10.
Notification Only
You can use a script named Test located in the failover scripts folder to control
whether, in the event of a failover condition, the secondary server acquires the primary
server’s IP address, or simply sends an email notification. If no script exists, or if the
script returns a zero result, then the secondary server acquires the primary’s IP address.
If the script returns a nonzero result, then the secondary server skips IP address
acquisition and only sends email notification of the failover condition. The
Test script is
run to determine whether the IP address should be acquired and to determine if the IP
address should be relinquished when the primary server returns to service.
A simple way to set up this notification-only mode is to copy the script located at
/usr/bin/false to the folder named with your primary server IP address, and then
change the name of the script to Test. This script always returns a nonzero result.
Using the Test script, you can configure the primary server to monitor the secondary
server and send email notification if the secondary server becomes unavailable.
Pre and Post Scripts
You can configure the failover process with scripts that can run before acquiring the
primary IP address (pre acquisition), after acquiring the IP address (post acquisition),
before relinquishing the primary IP address (pre relinquish), and after relinquishing the
IP address back to the primary server (post relinquish). These scripts reside in the
/Library/IPFailover/IP_address folder on the secondary server. The scripts use these four
prefixes:
 PreAcq—Run before acquiring the IP address from the primary server
 PostAcq—Run after acquiring the IP address from the primary server
 PreRel—Run before relinquishing the IP address back to the primary server
 PostRel—Run after relinquishing the IP address back to the primary server
Important: Always be sure that the primary server is up and functioning normally
before you activate IP failover on the secondary server. If the primary server isn’t
sending broadcast messages, the secondary server will initiate the failover process and
acquire the primary’s public IP address.
You may have more than one script at each stage. The scripts in each prefix group are
run in the order in which their file names appear in a folder listing using the
ls tool.