Managing Serviceguard Extension for SAP Version B.05.10, December 2012

Figure 4 Failover Node with Application Server package
Figure 4 illustrates a common configuration with the adoptive node running as a Dialog Server
during normal operation. Node1 and node2 have equal computing power and the load is evenly
distributed between the combination of database and Central Service Instance on node1 and the
additional Dialog Instance on node2. If node1 fails, the Dialog Instance package will be shut down
during failover of the dbciSID package. This is similar to a one-package setup without Dialog
Instance packaging.
The advantage of this setup, after repair of node1, is the Dialog Instance package can be restarted
on node1 instead of node2. This saves downtime that would otherwise be necessary caused by
a failback of the dbciSID package. The two instances can be separated to different machines
without impacting the production environment negatively. It should be noted that for this scenario
with just two hosts there is not necessarily a requirement to enable automatic failover for the Dialog
Instance package.
The described shutdown operation for Dialog Instance packages can be specified in any SGeSAP
legacy package directly. In modularized SGeSAP, it is recommended to use generic Serviceguard
package dependencies instead.
Handling of Redundant Dialog Instances
Non-critical SAP Application Servers can be run on HP-UX, Novell SLES or RedHat RHEL Linux
application server hosts. These hosts do not need to be part of the Serviceguard cluster. Even if
the additional SAP services are run on nodes in the Serviceguard cluster, they are not necessarily
protected by Serviceguard packages. A combination of Windows/HP-UX application servers is
technically possible, but additional software is required to access HP-UX filesystems or HP-UX-like
remote shells from the Windows system.
All non-packaged ABAP instances are subsequently called Additional Dialog Instances or sometimes
synonymously Additional SAP Application Servers to distinguish them from mission-critical Dialog
Instances. An additional Dialog Instance that runs on a cluster node is called an Internal Dialog
Instance. External Dialog Instances run on HP-UX or Linux hosts that are not part of the cluster. Even
16 Designing SGeSAP Cluster Scenarios