Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Designing Highly Available Cluster Applications
Designing Applications to Run on Multiple Systems
Appendix B 327
Designing Applications to Run on Multiple
Systems
If an application can be failed to a backup node, how will it work on that
different system?
The previous sections discussed methods to ensure that an application
can be automatically restarted. This section will discuss some ways to
ensure the application can run on multiple systems. Topics are as
follows:
• Avoid Node Specific Information
• Assign Unique Names to Applications
•Use Uname(2) With Care
• Bind to a Fixed Port
• Bind to a Relocatable IP Addresses
• Give Each Application its Own Volume Group
• Use Multiple Destinations for SNA Applications
• Avoid File Locking
Avoid Node Specific Information
Typically, when a new system is installed, an IP address must be
assigned to each active network interface. This IP address is always
associated with the node and is called a stationary IP address.
The use of packages containing highly available applications adds the
requirement for an additional set of IP addresses, which are assigned to
the applications themselves. These are known as relocatable
application IP addresses. Serviceguard’s network sensor monitors the
node’s access to the subnet on which these relocatable application IP
addresses reside. When packages are configured in Serviceguard, the
associated subnetwork address is specified as a package dependency, and
a list of nodes on which the package can run is also provided. When
failing a package over to a remote node, the subnetwork must already be
active on the target node.