Creating a CICS topology

When you create a CICS® topology for the application, separate the application into components for presentation, business logic, and data access.

Before you begin

To follow the scenario, you must have an application that runs in a single CICS region. This scenario uses the general insurance application, which is initially set up to run in a single region. To use the general insurance application, you must have completed the setup as described in The general insurance application.

About this task

Using a topology has the following benefits:

You can create a highly available application
You can introduce workload management
You can scale the application by cloning additional regions to cope with an increase in throughput

To create a simple topology, create three CICS regions: a terminal-owning region (TOR), an application-owning region (AOR), and a data-owning region (DOR). You can use MRO or IPIC connections between the CICS regions, but MRO is faster when the regions are in the same sysplex. You do not have to change the database or VSAM files.

In this scenario, you can reuse the existing region that contains the application as the TOR. You can copy the startup JCL and edit it to change the system initialization parameters; for example, the TOR does not require a connection to DB2® so you can remove the DB2CONN system initialization parameter.

Procedure

Run the @CDEF122 job to create the definitions for the topology in the shared CSD.
Copy and edit the JCL for the stand-alone region to create a TOR, an AOR, and a DOR.
The JCL is already configured to use the named counter pool that is required by the application.
1. In each copy of the JCL, add the application load library to the DFHRPL concatenation:
```
userid.CB12.LOAD
```
2. In the JCL for the TOR, add the following system initialization parameter values:
```
GRPLIST=(DFHLIST,TORLIST)
DB2CONN=NO
ISC=YES
```
  You can reuse the existing stand-alone region as the TOR if preferred.
3. In the JCL for the AOR, add the following system initialization parameter values:
```
GRPLIST=(DFHLIST,AORLIST)
DB2CONN=NO
ISC=YES
```
4. In the JCL for the DOR, add the following system initialization parameter values:
```
GRPLIST=(DFHLIST,DORLIST)
ISC=YES
DB2CONN=YES
```
Split the application across the regions. Put the presentation layer in the TOR, the business logic in the AOR, and the data management in the DOR. The PROGRAM resources in each region have a remote system with the name of the connection to access parts of the application over the network.
The general insurance application is already componentized to run in different regions. For your own applications, you might need to work with the application developer and architect to ensure that the application can run across CICS regions in this way.
Create connections between the CICS regions:
1. In the TOR, create CONNECTION and SESSIONS definitions with the name AOR1 to point to the AOR.
  Set the following attributes on the CONNECTION definition:
```
CONNECTION(AOR1) 
GROUP(GENATOR) 
NETNAME(netname)
AUTOCONNECT(YES) 
ACCESSMETHOD(IRC) 
ATTACHSEC(IDENTIFY)
```
  Set the following attributes on the SESSIONS definition:
```
SESSIONS(AOR1) 
GROUP(GENATOR) 
CONNECTION(AOR1)
PROTOCOL(LU61) 
RECEIVECOUNT(50)
AUTOCONNECT(YES) 
SENDCOUNT(50)
RECEIVEPFX(R) 
SENDPFX(S) 
```
2. In the AOR, create CONNECTION and SESSIONS definitions with the name TOR1 to point to the terminal-owning region, and CONNECTION and SESSIONS definitions with the name DOR1 to point to the DOR.
  Set the following attributes on the CONNECTION definition for the TOR:
```
CONNECTION(TOR1) 
GROUP(GENAAOR) 
NETNAME(netname) 
AUTOCONNECT(YES) 
ACCESSMETHOD(IRC) 
ATTACHSEC(IDENTIFY)
```
  Set the following attributes on the SESSIONS definition for the TOR:
```
SESSIONS(TOR1) 
GROUP(GENAAOR) 
CONNECTION(TOR1) 
PROTOCOL(LU61) 
RECEIVECOUNT(50) 
AUTOCONNECT(YES) 
SENDCOUNT(50) 
RECEIVEPFX(R) 
SENDPFX(S) 
```
3. In the DOR, create CONNECTION and SESSIONS definitions with the name AOR1 to point to the AOR.
  Set the following attributes on the CONNECTION definition:
```
CONNECTION(AOR1) 
GROUP(GENATOR) 
NETNAME(netname)
AUTOCONNECT(YES) 
ACCESSMETHOD(IRC) 
ATTACHSEC(IDENTIFY)
```
  Set the following attributes on the SESSIONS definition:
```
SESSIONS(AOR1) 
GROUP(GENATOR) 
CONNECTION(AOR1)
PROTOCOL(LU61) 
RECEIVECOUNT(50)
AUTOCONNECT(YES) 
SENDCOUNT(50)
RECEIVEPFX(R) 
SENDPFX(S) 
```
Log in to the TOR and run the transaction SSC1 to inquire on some customer records.

Results

The application request goes through the CICS regions in the topology and accesses VSAM and DB2. The resulting architecture is represented in the following diagram:

Diagram shows three connected CICS regions accessing a shared CSD. The terminal-owning region contains the presentation logic for the application. The application-owning region contains the business logic. The data-owning region access the VSAM file and DB2. The application-owning region and data-owning region also both access the coupling facility. — Figure 1. CICS topology connected by MRO

What to do next

Although the application is running in a CICS topology, each region has static definitions that must be manually updated. In addition, no workload management can occur. By managing the CICS regions with CICSPlex® SM, you can add workload management to replace the static definitions with dynamic routing. You can also add regions to scale the topology, providing additional resiliency in the CICSplex.