82 WebSphere for z/OS Connectivity Architectural Choices
One consideration that must be reviewed with this configuration is the possibility
of a storm drain. If the connection from WebSphere to the CICS Routing Region
or the Routing Region itself is lost, then that WebSphere server will appear to
have better performance and the Sysplex Distributor and WLM will direct work
towards it. There are ways to reduce this concern discussed in the section 3.8,
“Routing CICS local to remote” on page 72
.
3.10.1 Remote availability with CICS routing: Attributes
Figure 3-17 High availability remote connection with routing region
Performance
This configuration in Figure 3-17 takes advantage of the performance
enhancements offered by Sysplex Distributor and WLM for WebSphere, and is
identical to the last configuration. The major difference between this
configuration and the last is the use of the local CICS TG to WebSphere and the
use of CICS Routing Region in the LPAR.
This local connection to the routing region provides better performance then the
remote connection and supports two-phase commits. The second advantage is
the routing region (CICSPlex SM) provides true dynamic routing to the AOR
providing better performance. Multiregion operation (MRO) connectivity between
LPARs generally has better performance than TCP/IP.
Performance
WebSphere can use SD and WLM to
meet LPAR performance goals
Implements CICS best practice
solution for performance management
Takes advantage of WebSphere
access to local CICS routing region for
performance
Uses CICS routing program to access
multiple AORs with low system
overhead
Availability
Provides greatest amount of
availability due to no single point of
failure
CICSPlex SM can provide enhanced
routing and availability capabilities
Security
Same security considerations as
discussed in “Routing CICS local to
remote”
z/OS
z/OS
SYSPLEX
CICSPlex/SM
z/OS
z/OS
Transactional capabilities
If CICS TG is local to WebSphere then
full two-phase commit across all
systems
Scalability
Local WebSphere or CICS can be
vertically scaled (CPU, memory,
channels, …)
Chapter 3. CICS connectivity options 83
The previous configuration using Sysplex Distributor and DVIPA only provided
dynamic connection to the AOR with the best performance at the time of
connection. After the connection was established, the routing was static through
the life of the connection regardless of the performance of the CICS AORs. Like
the last configuration, the performance of the CICS portion of this configuration is
well understood. To establish the SLA for the total system, WebSphere portion
can be scaled to meet the performance goals. The total system performance can
be managed using a combination of Sysplex Distributor and WLM for
WebSphere and CICSPlex SM for the CICS portion of the system.
Availability
CICSPlex SM is the best practice for connecting WebSphere to CICS. This
architecture builds on Switch local to remote architecture. That architecture
provides CICS application availability through CICS dynamic routing. The
WebSphere CICS system availability is increased by adding Sysplex Distributor
with WLM in front of WebSphere. This eliminates WebSphere from being a single
point of failure by allowing Sysplex Distributor to route traffic to the alternate,
available Websphere Application Server.
The use of one CICS TG and CICS Routing Region could possibly become a
single point of failure and a possible storm drain. To solve this problem, a second
CICS TG and CICS Routing Region should be created. Then ARM can be used
to restart the CICS listener very quickly.
If this is not acceptable in your environment, multiple listeners can be
implemented using the EXCI user-replaceable module DFHXCURM.
DFHXCURM provides for simple fail-over and round-robin workload balancing by
providing a means to capture retryable errors and modify the destination APPLID
specified in the EXCI call.
Security
There are security advantages to using a CICS router. If you use a CICS TG, you
have no possibility to customize security in the CICS TG environment. It is pretty
much a black box. But when you use a CICS router, you have a lot more
possibilities. For example, CICSPlex SM allows you to add your own code to the
routing decision in EYU9WRAM.
Transactional capabilities
This architecture provides full two-phase commit across WebSphere and CICS
environments if the CICS TG is implemented local to WebSphere with CICS
routing region in the same LPAR. This solution is attractive because two-phase
commit is not limited to the local z/OS image or even sysplex. The CICS AOR
can be on any z/OS system. CICS with the use of the routing region will
coordinate the commit for all CICS resources.

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