HP-UX SNAplus2 R7 Administration Guide

Appendix DUsing SNAplus2 in a High Availability Environment
make highly available. Identify at least two SNAplus2 servers that can provide SNA network connectivity in your
ServiceGuard cluster. Consequently, if one server experiences a failure that prevents it from providing SNA network
connectivity, another server can take over that role. Follow these steps to help you build your SNAplus2 package:
1. List all of the mission critical applications that use SNAplus2 for SNA network connectivity.
2. Diagram your network topology so that you know the location of the servers that are part of the ServiceGuard
cluster and any other systems needed for SNA network connectivity.
3. List the SNAplus2 LSs that must be highly available. The SNAplus2 LSs are what will be monitored by
ServiceGuard to determine if the HP 9000 server is providing SNA network connectivity. If all of the highly
available SNAplus2 LSs are active, the server is providing SNA network connectivity.
4. Identify a primary server and one or more backup servers for the SNAplus2 package. When the primary server
fails to provide SNA network connectivity (that is, the SNAplus2 LS is no longer active), ServiceGuard will
automatically migrate the package to another server system.
Note that to simplify the package migration during failure episodes, we recommend that you run only one
SNAplus2 package in your ServiceGuard cluster; that is, at any one time, only one system in a ServiceGuard
cluster will be running a highly available SNAplus2 LS. Backup systems in your cluster can provide SNAplus2
services for non-mission critical applications.
5. Define how the mission critical applications will be impacted by the migration from one server to another. Since
LU-LU sessions will be lost, specify what you will be required to do to re-activate an LU-LU session through
another server system. If an application needs to be restarted after a server system failure (perhaps because the
application runs on the server), determine if you want ServiceGuard to automate the application startup.
6. Create a set of commands that ServiceGuard will issue when an SNAplus2 LS fails so that the migration to a
backup server happens smoothly. Make sure this set of commands contain
halt commands to free SNAplus2
resources on the primary server and run commands to activate the necessary resources on the backup server.
Figure D–4, SNAplus2 on Primary and Backup Servers (shown previously) illustrates these steps. The picture shows
the network topology including the SNAplus2 servers and clients. The mission critical applications are APPC
TPs. The SNAplus2 LS that is highly available is HALS. The primary server is hp_pri and the backup server is
ha_back. Assuming the applications attempt to activate a new LU-LU session when they lose the LU-LU session
they were using, you simply need to wait for the migration to occur. The applications require no restarting because
they run on client systems. The set of commands needed to start HALS on the backup server are listed. Once the
backup server reactivates HALS, the applications will again be able to obtain LU-LU sessions.
D.3.3 SNAplus2 Package
To integrate SNAplus2 into your ServiceGuard cluster, an SNAplus2 package must be defined. Defining an SNAplus2
package tells ServiceGuard that the SNAplus2 software on the HP 9000 server must be highly available, and access
to the SNA network is mission critical. Defining an SNAplus2 package will allow ServiceGuard to do the following:
• Automatically start the SNAplus2 software when the SNAplus2 package starts
• Automatically start a process to monitor the state of the SNAplus2 software on the server
• Automatically migrate the SNAplus2 package to a backup server if the package ever fails to provide SNA
network connectivity
ServiceGuard will monitor the health of the SNAplus2 package, and migrate the package to another server if it
should ever fail to provide SNA network connectivity.
Several configuration steps are involved in defining packages. Follow the ServiceGuard product documentation
for planning and beginning the package definition. ServiceGuard allows you to create a package using SAM or
using HP-UX commands and editors. The following suggestions will help you create your SNAplus2 ServiceGuard
package.
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