User guide

202 ExtremeWarePx1 1.2 Command Reference Guide
Health-Check Commands
You can change the global default values for these properties. In addition, you conÞgure these
properties for each server group. The same property values are used for all servers in a given server
group.
If health checks are enabled, and you do not speciÞcally conÞgure a particular property for a particular
server group, that group uses the propertyÕs global default value.
If you change the global default value for any property, the new global default will be used by any
server group that did not speciÞcally conÞgure that particular.
If the CPU is swamped by too many health checks or other tasks, the interval and retry-interval times may
be stretched. By design, health checks are randomized. The average interval between two consecutive
health checks is interval; however, any individual check is performed using a minor randomized interval
of interval plus or minus 50%. The actual interval between any particular pair of consecutive health
checks may be as short as interval / 2 or as long as interval * 3 / 2.
Health Check Procedure
The health check procedure:
1 As soon as the system comes up or a server is enabled, a health check is performed on the server. If
it passes, the server goes into service immediately; if not, it remains out of service.
2 As long as the server is in service, the health check is repeated every interval seconds. If the server
passes a health check, it remains in service; if it fails, it is removed from service.
3 If the server fails a health check, it is rechecked after retry-interval seconds.
Ñ If a recheck fails, the recheck is repeated after retry-interval seconds. After fail-after
consecutive failures, the server is removed from service.
Ñ If a recheck succeeds, the recheck is repeated after retry-interval seconds. After restore-after
consecutive successes, the server is put into service.
ARP Checks
In addition to the health check described in the preceding sections, an additional check is performed
automatically for servers on the same network as the application switchÕs system IP. In this situation,
the switch sends periodically sends ARP requests to each server in its network. The switch uses
information in the ARP response when it sends trafÞc to servers on the local network
The global property arp-interval controls the frequency with which ARP checks are performed. This
property is initially set to 5 minutes; that is, an ARP signal is send to a server in the same network as
the system IP every 5 minutesÑin addition to any ping, TCP open, or HTTP health check that is
conÞgured for the sever.
You can change the value of the arp-interval property with the configure health-check arp-interval
command.