Managing Serviceguard Extension for SAP on Integrity Linux, December 2005

Understanding Serviceguard Extension for SAP on Integrity Linux
Application Servers
Chapter 1 15
Application Servers
The database and the SAP central instance are always running on nodes
that are protected by Serviceguard.
Other SAP services can be run on Linux application server hosts. These
hosts can be but must not need to be part of the Serviceguard cluster. If
the additional SAP application servers are run on nodes inside the
Serviceguard for Linux cluster, they can be protected by Serviceguard for
Linux.
All application servers different from the central instance are called
additional application servers. An additional application server that runs
on a cluster node is called an internal application server. External
application servers run on hosts that are not part of the cluster. Even if
application servers are external to the cluster, they are affected by
package startup and shutdown.
SAP services like dialog, update, batch, spool, and gateway, are usually
run on additional application servers. Services like the message or
enqueue service should not be configured to run on additional application
servers. Only one message server and one enqueue server is configured
for each SAP system and contained in the SAP central instance.
The message server, enqueue server, database and NFS server are all
single points of failure (SPOF). To maintain high availability, all these
SPOFs for the SAP system must be eliminated by configuring them in
Serviceguard for Linux cluster nodes.
In standard SAP scenarios the SPOFs database, NFS, message and
enqueue server are all protected. It is highly recommended that at least
one instance of each additional SAP service in the Serviceguard for
Linux cluster is protected.