The following diagram shows an example CICSplex consisting of four CICS
regions, each executing on separate OS/390® machines within a sysplex.
Figure 1. CICSplex using DNS connection
optimization
The MVS systems are named MVS1A, MVS1B, MVS1C and MVS1D, with the CICS
regions having APPLIDs of CICSPROD1, CICSPROD2, CICSDEV1 and CICSDEV2
The sysplex is defined to the DNS to have the name PLEX1 and each MVS machine
has a single IP address. The above diagram describes the names that a client
machine could use to access the CICS regions based on the following resource
definitions installed on each CICS:
- The region CICSPROD1 running on machine MVS1A has twoTCPIPSERVICE definitions,
one specifying a group_name of WWW and the second specifying a group_name
of IIOP1.
- The region CICSPROD2 running on machine MVS1B has one TCPIPSERVICE definition,
specifying a group_name of WWW.
- The region CICSDEV1 running on machine MVS1C has two TCPIPSERVICE definitions,
one specifying a group_name of IIOP1 and the second specifying a group_name
of WWWDEV.
- The region CICSDEV2 running on machine MVS1D has one TCPIPSERVICE definition,
specifying a group_name of WWWDEV.
The names that a client can access are:
- PLEX1.IBM®.COM—returns the IP address of any of the machines in the sysplex.
- WWW.PLEX1.IBM.COM—returns either the address of MVS1A or MVS1B.
- IIOP1.PLEX1.IBM.COM—returns either the address of MVS1A or MVS1C.
- WWWDEV.PLEX1.IBM.COM—returns either the address of MVS1C or MVS1D.
You can also address individual CICS regions within a group by using their
APPLIDs (or server names). For example, CICSPROD1.WWW.PLEX1.IBM.COM will return
the address of MVS1A. This is equivalent to MVS1A.PLEX1.IBM.COM, but the
client does not have to know the machine on which the CICSPROD1 server is
running, only that CICSPROD1 is part of the WWW group.
Since these names dynamically become available as CICS regions register
with the WLM, adding more CICS regions and more MVS machines does not result
in any more administration. Using the generic host names (such as WWWDEV.PLEX1.IBM.COM)
decouples client applications from specific CICS regions and MVS hosts, which
enhances availability and scalability.