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Configuring z/OSMF for high availability in Sysplex

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Configuring z/OSMF for high availability in Sysplex

z/OSMF high availability (HA) should be configured in Hot Standby mode to ensure availability of REST services. The goal of this configuration is to ensure that one z/OSMF server is always available to provide the REST services.

In Hot Standby mode, there is at least one backup (hot-standby) server and a preferred target server. Both targets are active, and both z/OSMF servers are bound to the DVIPA. The preferred z/OSMF server receives all new incoming requests. When the preferred z/OSMF server fails or the system becomes down, new requests are routed to the backup (hot-standby) server. The distributing DVIPA does not perform load balancing of requests across multiple systems. For more information, read the following articles in IBM Documentation:

Sysplex environment requirements​

Before you begin, ensure that the Sysplex environment meets the following requirements for z/OSMF REST services:

Setting up z/OSMF nucleus​

This information is intended for a first-time z/OSMF setup. Follow these high-level steps to create a z/OSMF nucleus on your system.

For detailed information about each step, see Create a z/OSMF nucleus on your system in IBM Documentation.

  1. Create the z/OSMF security authorizations by running the sample JCL SYS1.SAMPLIB(IZUSEC). z/OSMF security authorizations will be used by all z/OSMF servers across multiple systems.

  2. Create a shared file system per z/OSMF server by running the sample JCL SYS1.SAMPLIB(IZUMKFS). It holds configuration settings and the persistence data.

  3. Copy the Sample Parmlib Member SYS1.SAMPLIB(IZUPRM00) to PARMLIB and modify it according to requirements of z/OSMF HA parmlib member in Sysplex. Each system uses a different IZUPRMxx member. For example, IZUPRM0A and IZUPRM0B.

  4. Copy the following z/OSMF procedures from SYS1.PROCLIB into your JES concatenation:

    • IZUSVR1 (Each z/OSMF server should use the different started procedure. For example, IZUSVRA and IZUSVRB.)
    • IZUANG1
    • IZUFPROC

  5. Define different STARTED profiles for z/OSMF servers.

Requirements of z/OSMF HA parmlib member in Sysplex​

  • AUTOSTART_GROUP, more than one z/OSMF server (independent z/OSMF instances) is to be autostarted in a Sysplex. For instance, System A will autostart a server and similarly, System B will autostart the second z/OSMF server.

    z/OSMF has a default autostart group (IZUDFLT) which is used in monoplex or single z/OS image. To have more z/OSMF servers autostarted in a Sysplex, you must associate each server and the systems it serves with a unique autostart group name. For example, AUTOSTART_GROUP('IZUDFLA') for System A and AUTOSTART_GROUP('IZUDFLB') for System B

  • AUTOSTART(LOCAL) should be used by all z/OSMF instances.

  • HOSTNAME, the DVIPA address will be used as the z/OSMF host name for all instances.

  • HTTP_SSL_PORT, all servers are listening on the same port.

  • KEYRING_NAME, all servers should use the same key ring such as IZUKeyring.IZUDFLT.

  • SERVER_PROC, each z/OSMF server should use the different started procedure. For example, IZUSVRA and IZUSVRB.

  • ANGEL_PROC, all z/OSMF servers can connect to the same z/OSMF angel process such as IZUANG1.

  • SAF_PREFIX, they should use the same SAF profile prefix such as IZUDFLT.

  • USER_DIR, each instance uses a shared file system with a unique mount point for each AUTOSTART group that be automatically started. For example, /global/zosmf/zosmfa and /global/zosmf/zosmfb.

Configuring z/OSMF for high availability​

The following DVIPA configuration ensures the availability of z/OSMF for Hot-Standby. For example, suppose that you have a Sysplex of two z/OS systems: A, B.

  1. Enable dynamic XCF on each host by adding the following TCP/IP definitions:

    • IPCONFIG SYSPLEXROUTING DYNAMICXCF x.x.x.A 255.255.255.0 1 for SYSA
    • IPCONFIG SYSPLEXROUTING DYNAMICXCF x.x.x.B 255.255.255.0 1 for SYSB

  2. Define a dynamic VIPA (DVIPA) for both systems:

     VIPADYNAMIC                                                      
      VIPADEFINE  255.255.255.0 x.x.x.V
      VIPADISTRIBUTE DEFINE DISTM HOTSTANDBY x.x.x.V 
        PORT 443 DESTIP
         x.x.x.A  PREFERRED 
         x.x.x.B  BACKUP                                         
     ENDVIPADYNAMIC

    where,

    • x.x.x.A is the home address for SYSA.
    • x.x.x.B is the home address for SYSB.
    • x.x.x.V is Dynamic VIP Address.

The VIPADISTRIBUTE statement with PREFERRED and BACKUP settings is used to enable automatic dynamic VIPA takeover to occur, if needed.

Both z/OSMF servers are bound to the DVIPA x.x.x.V. With both z/OS systems active in the Sysplex, the preferred z/OSMF server, SYSA receives all new incoming requests. If SYSA fails, new work requests for z/OSMF are routed to the server on SYSB. When SYSA resumes normal operations, new work requests for z/OSMF are routed to SYSA again. This is the default behavior because the AUTOSWITCHBACK parameter of the VIPADISTRIBUTE statement is in effect by default.

If you do not want the distributor to switch back to the preferred target when it becomes available, you can specify the NOAUTOSWITCHBACK parameter for the VIPADISTRIBUTE statement.

VIPADYNAMIC                                                      
  VIPADEFINE  255.255.255.0 x.x.x.V
  VIPADISTRIBUTE DEFINE DISTM HOTSTANDBY NOAUTOSWITCHBACK x.x.x.V 
     PORT 443 DESTIP
        x.x.x.A  PREFERRED 
        x.x.x.B  BACKUP                                         
ENDVIPADYNAMIC

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