HP Serviceguard Extension for SAP (SGeSAP) manual Handling of Redundant Dialog Instances

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