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

Example: A simple mutual failover scenario for an ABAP application defines two packages, called
dbSID and ascsSID (or ciSID for old SAP releases).
Robust Failover Using the One Package Concept
In a one-package configuration, the database, NFS and SAP SPOFs run on the same node at all
times and are configured in one SGeSAP package. Other nodes in the Serviceguard cluster function
as failover nodes for the primary node on which the system runs during normal operation.
To maintain an expensive idle standby is not required. SGeSAP allows to utilize the secondary
node(s) with different instances during normal operation. A common setup installs one or more
non-mission critical SAP Systems on the failover nodes, typically SAP Consolidation, Quality
Assurance, or Development Systems. They can gracefully be shutdown by SGeSAP during failover
to free up the computing resources for the critical production system. For modular packages, the
sgesap/sapextinstance module can be added to the package to allow specifying this kind
of behavior.
Development environments tend to be less stable than production systems. This should be taken
into consideration before mixing these use-cases in a single cluster. A feasible alternative would
be to install Dialog Instances of the production system on the failover node.
If the primary node fails, the database and the Central Instance fail over and continue functioning
on an adoptive node. After failover, the system runs without any manual intervention needed. All
redundant Application Servers and Dialog Instances, even those that are not part of the cluster,
can stay up or be restarted (triggered by a failover). A sample configuration in Figure 2 shows
node1 with a failure, which causes the package containing the database and central instance to
fail over to node2. A Quality Assurance System and additional Dialog Instances get shut down,
before the database and Central Instance are restarted.
Figure 2 One-Package Failover Scenario
12 Designing SGeSAP Cluster Scenarios