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152 Chapter 13 Working With Network Services
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 directory 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 directory to control
whether, in the event of a failover condition, the secondary server acquires the
primary’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 non-zero 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 directory named with your primary server IP address and then
change the name of the script to “Test”. This script always returns a non-zero 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 (preacquisition), after acquiring the IP address (postacquisition),
before relinquishing the primary IP address (prerelinquish), and after relinquishing the
IP address back to the primary server (postrelinquish). These scripts reside in the
/Library/IPFailover/<IP address> directory on the secondary server, as previously
discussed. The scripts use these four prefixes:
• PreAcq – run before acquiring IP address from primary server
• PostAcq – run after acquiring IP address from primary server
• PreRel – run before relinquishing IP address back to primary server
• PostRel – run after relinquishing IP address back to 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 their file names appear in a directory listing using the ls command.
LL2354.book Page 152 Monday, October 20, 2003 9:47 AM