Figure 1 shows a z/OS® sysplex containing four systems, a name server external to the sysplex, a name server in the sysplex, and several clients in the network. The z/OS Load Balancing Advisor and ADNR are running on one of the systems in the sysplex. An instance of the z/OS Load Balancing Agent is active on three of the sysplex systems. Three instances of a server application are active within the sysplex.
ADNR is configured with information about sysplex resources to which you want to assign DNS names. These resources are configured on a group basis. For example, to have ADNR manage DNS names in a name server for a sysplex containing several instances of a CICS® listener application, all potential CICS listener instances for a given port in the sysplex are defined under the same group in the ADNR configuration file.
ADNR registers its configured information about sysplex resources with a z/OS Load Balancing Advisor application. The Advisor application disseminates this information to the z/OS Load Balancing Agents (Agents), which report back to the Advisor about the availability of the resources registered by ADNR. The Advisor then reports back to ADNR about which of its registered resources are active and which are not. The Advisor subsequently reports to ADNR any changes in the availability of those resources.
For each group of resources that the Advisor reports as available, ADNR adds a DNS name to the name server that represents the entire group of resources in that group, and maps that name to the IP addresses of the available resources in that group. Continuing with the CICS listener example, the IP address of each active CICS listener application is mapped to the name representing the entire group of CICS listener applications. The IP address of each inactive CICS application is not mapped to that DNS name. Clients then connect to their application using the name that ADNR added to the name server. The address or addresses returned to the client's resolver reflect only active application instances. Thus, the client can use one DNS name to connect to any active instance of an application. As application instances become unavailable, the addresses of those unavailable application instances are disassociated from that DNS name in the name server. If all application instances in that group become unavailable, the DNS name representing that group of applications is removed from the name server.
You can also configure ADNR to update the name server with the names of individual server instances, which map to IP addresses that can be used to reach those server instances as those server instances become available. Thus, if a client needs to connect to a specific server instance, that name can be used to make the connection. As each individual server instance becomes unavailable, the DNS name representing the unavailable server instance is removed from the name server.
The name servers that ADNR manages must support RFC 2136, Dynamic Updates in the Domain Name System (DNS UPDATE). For information about accessing RFCs, see Related protocol specifications.
For administrative purposes, it is advantageous to run ADNR within the same sysplex as the resources it manages. Run ADNR in a sysplex so that it can be moved to provide optimal availability. You can reduce network traffic between ADNR and the Advisor by running ADNR on the same system where the Advisor is running. In addition, the possibility of network outages disrupting communication between ADNR and the Advisor is eliminated by this configuration.