The timing of the reach advisor may affect when a takeover occurs in a High Availability configuration
 Technote (troubleshooting)
 
Problem(Abstract)
Even though both the primary and backup load balancer machines recognize that a server is marked down, the timing of when the server is marked down in the reach advisor might cause a takeover.
 
Cause
The takeover occurs because the backup Load Balancer can hit more reach targets than the primary load balancer in a High Availability configuration.
 
Resolving the problem
The reach advisor will ping all servers in the load balancer configuration. It will also ping a target added by the high availability reach command. If a server can not be pinged, the reach advisor will time out in 2 seconds and will retry up to 3 times. If there are a large number of servers then the likelihood of the primary and backup load balancers having a different status increases.


If the backup load balancer has pinged a server and marked it up, and then continues through the list, it is possible that the primary load balancer will start its reach interval and then see that the server is now down. The backup would then show that it can hit more reach targets and cause a takeover to occur. This is normal operation and working as intended.


The High Availability function is designed to keep the product up and forwarding traffic. So when the backup detects that it can hit more reach targets it will takeover. This is functioning correctly. The only way to avoid the takeover would be to have both reach advisors synchronized so that both the primary and backup load balancers mark the server down at the same time. The overhead involved to do this would be too high to make this a viable solution.

 
 
 


Document Information


Product categories: Software > Application Servers > Distributed Application & Web Servers > WebSphere Application Server > Edge Component
Operating system(s): Windows
Software version: 6.1
Software edition:
Reference #: 1246872
IBM Group: Software Group
Modified date: Sep 29, 2006