Brocade Communications Systems 12.4.00 manual

1 Enabling DNS request logging

SITE-ServerIronADX# debug distributed-hcheck sent-add-list GSLB: sent-add-list debugging is on

SITE-ServerIronADX#

Sending Address List msg: VIP = 192.9.2.16, Active = 1, Host Range = 1, Num Ports = 2

Sending Address List msg: VIP = 192.9.2.17, Active = 0, Host Range = 1, Num Ports = 3

Sending Address List msg: done

Impact of distributed health checks on the Flashback metric

If the GSLB ServerIron ADX supports the distributed health check feature, then the Flashback metric is disabled by default in release 08.1.00S. Flashback is defined as the round-trip time for a health check sent by the GSLB ServerIron ADX to the host application on the server. Flashback delay is computed as the round-trip time of the Layer 4 health check to the TCP port and the round-trip time for the Layer 7 health check for the application. If the GSLB ServerIron ADX supports the distributed health check feature, then the Flashback metric is disabled by default. The reason for this is that the distributed health GSLB ServerIron ADX does not carry out health checks for the host servers load balanced by the distributed health check site ServerIron ADXs; instead the site ServerIron ADXs periodically report this health check status information to the GSLB ServerIron ADX. Note that the distributed health check GSLB ServerIron ADX still maintains health checks for the host servers behind the non-distributed health check site ServerIron ADXs. Thus the distributed health check GSLB ServerIron ADX maintains health checks and computes the Flashback delay only for host servers behind the non-distributed health check site Servers. Since Flashback delay is not relevant and not computed for all the host servers, the Flashback metric is disabled by default if the GSLB ServerIron ADX supports the distributed health check feature.

Flashback metric can be enabled on the distributed health check ServerIron ADX if required. This should be done with caution. You should enable the Flashback metric only if he or she is certain that all the peer site ServerIron ADXs support non-distributed health check only i.e. they do not support the distributed health check feature. In such a case, the health check for all of the host servers will be maintained by the GSLB ServerIron ADX and each of them will have an associated Flashback value.

NOTE

The Flashback delay value for the VIPs on site ServerIron ADXs that support the distributed health check feature will be displayed as “0” in the GSLB show commands. This implies that there is no Flashback delay value associated with that IP address.

108	ServerIron ADX Global Server Load Balancing Guide
	53-1002437-01