User's Guide

Dialog Instance virtualization packages provide high availability and flexibility at the same time. The system
becomes more robust using Dialog Instance packages. The virtualization allows moving the instances manually
between the cluster hosts on demand.
Figure 1-4 Failover Node with Application Server package
Figure 1-4 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 is, that after repair of node1, the Dialog Instance package can just 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, SUSE or RedHat 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 if Dialog Instances are
external to the cluster, they may be affected by package startup and shutdown.
18 Designing SGeSAP Cluster Scenarios