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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 website 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 the rsync man pages for more information.
Requirements
IP failover isn’t a complete solution; it is one tool you can use to increase your server’s availability to your clients. To use IP failover, you will need to set up the following hardware and software.
Hardware
IP failover requires the following hardware setup:
•Primary server
•Secondary server
•Public network (servers must be on same subnet)
•Private network between the servers (additional network interface card)
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:
•Unique IP addresses for each network interface (public and private)
•Software to mirror primary server data to secondary server
•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.
•If the broadcast is interrupted on both public and private networks, the secondary server initiates the failover process.
•If status messages are interrupted on only one network, the secondary server sends email notification of a network anomaly, but doesn’t acquire the primary server’s IP address.
Email notification is sent when the secondary server detects a failover condition, a network anomaly, and when the IP address is relinquished back to the primary server.
Chapter 13 Working With Network Services
