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360 Appendix D
Using SNAplus2 in a High Availability Environment
SNAplus2 High Availability Features
for high availability environments in that applications running on client
systems can access ports on multiple servers. By providing applications
with multiple paths to the remote SNA system, the client/server
configuration greatly reduces the number of single points of failure.
When an SNAplus2 application starts in a client/server configuration, it
tries to locate a suitable LU that is available. It queries all of the servers
that are active to see if one of them can provide an LU that has been
configured to be used by the application. If one of the servers provide s a
suitable LU, an LU- LU session is established between the server and
the remote SNA system. The SNAplus2 application can then access that
LU-LU session. It is important to note that the SNAplus2 application
does not specify which of the active servers should provide the LU. I t is
possible that more than one server can be configured to provide a
suitable LU.
There are two ways that more than one server can provide a suitable LU
to an SNAplus2 application running on a client system. First, the
application can be configured to use multiple LUs, and those LUs can be
spread across multiple HP 9000 servers. If the first LU is unavailable,
the application can request a different one. LU pools, if they contain LUs
that use multiple SNAplus2 LSs , can be used in this fashion. Similarly,
APPC transaction programs can be developed that access several local
LUs that are spread across multiple HP 9000 servers. Using this
technique, SNAplus2 applications can be given access to multiple paths
to the remote SNA system.