Apple Mac OS X Server (Administrator’s Guide) - Manual (Page 567)

Tools for Advanced Users 567
Enabling IP Failover
IP failover allows a secondary server to acquire the IP address of a primary server if the
primary server ceases to function. Once the primary server returns to normal operation, the
secondary server relinquishes the IP address. This allows your Web site to remain available
on the network even if the primary server is temporarily offline.
Note: IP failover only allows a secondary server to acquire a primary server’s IP address. You
need additional software tools such as rsync to provide capabilities such as mirroring the
primary server’s data on the secondary server. See rsync’s man pages for more information.
Requirements
IP failover is not a complete solution, rather one tool you can use to increase your server’s
availability to your clients. In order to use IP failover you will need to set up the following
hardware and software.
Hardware
IP failover requires the following hardware setup:
m primary server
m secondary server
m public network (servers must be on same subnet)
m private network between the servers (additional network interface card)
See “Setting Up a Private TCP/IP Network” on page 523 for more information on private
networks.
Note: Because IP failover uses broadcast messages, both servers must have IP addresses on
the same subnet of the public network. In addition, both servers must have IP addresses on
the same subnet of the private network.
Software
IP failover requires the following software setup:
m unique IP addresses for each network interface (public and private)
m software to mirror primary server data to secondary server
m scripts to control failover behavior on secondary server (optional)
Failover Operation
When IP failover is active, the primary server periodically broadcasts a brief message
confirming normal operation on both the public and private networks. This message is
monitored by the secondary server.
m If the broadcast is interrupted on both public and private networks, the secondary server
initiates the failover process.