Steps for configuring hot standby distribution

You can use hot standby distribution to have one preferred target server and one or more backup (hot standby) target servers. The preferred target server receives all new incoming connection requests and the hot standby servers act as backups in case the preferred target server becomes unavailable.

Perform the following steps to configure hot standby distribution on the VIPADISTRIBUTE statement:

1. Configure HOTSTANDBY on the DISTMETHOD parameter.
2. Configure the AUTOSWITCHBACK parameter or the NOAUTOSWITCHBACK parameter.
   • Configure AUTOSWITCHBACK if you want the distributor to automatically switch distribution back to the preferred target when it is available. For example, if the preferred target becomes a standby target because its server is no longer ready, when the server is again in the listening state, the distributor automatically switches back to the preferred target as the active target. This is the default value.
   • Configure NOAUTOSWITCHBACK if you want the distributor to continue to use a backup target when the preferred target is available.
     Rule: If NOAUTOSWITCHBACK is configured, then the active server is initially determined by order of activation; the first ready listener becomes the active server regardless of the configured server type (PREFERRED or BACKUP), and remains the active server unless it becomes unavailable.
3. Configure the HEALTHSWITCH parameter or the NOHEALTHSWITCH parameter.
   • Configure HEALTHSWITCH if you want the distributor to automatically switch from the active target when it is not healthy. This is the default. A target is not healthy when there is a severe problem detected by one of the following health metrics:
     • Target server responsiveness (TSR) value is 0%
     • Rate of abnormal transaction completions is 1000
     • General health of the application is 0%

     For more information, see Target server connection setup responsiveness monitoring, and the WLM health metric information in SERVERWLM - Distribution using WLM server-specific weights.

     Rule: When a switch occurs because a target is no longer healthy, the target is not used as a backup target even if its health recovers, unless all available backup targets have previously had health problems. Health metric indicators typically recover when a server is no longer receiving any work, and although a server can appear healthy, the distributor cannot determine if the server is actually healthy. When the distributor detects that the server is transitioning back to the ready state, it again uses the target as a backup.
     Tip: You can use the VARY TCPIP,,SYSPLEX,QUIESCE command and the VARY TCPIP,,SYSPLEX,RESUME command to manually bring a server back to the ready state. You can also use these commands before and after planned maintenance, or to temporarily divert new workload requests from a particular target. For more information, see Manually quiescing DVIPA sysplex distributor server applications.
   • Configure NOHEALTHSWITCH if you want the distributor to ignore health metrics. The distributor switches from the active target only when it is not ready or when the distributor does not have an active route to the target.
4. Configure the PREFERRED option or the BACKUP option after each XCF address on the DESTIP parameter to designate the preferred server and the backup servers, and configure a rank value for each backup server.
   • Configure PREFERRED to designate the preferred server. This must be configured for one, and only one, XCF address.
   • Configure BACKUP to designate a backup (hot standby ) server. This must be configured for at least one XCF address. Also configure a rank value on the BACKUP option for each backup server. The distributor switches to the highest ranked backup if the preferred server becomes unavailable.