Extreme Networks Px Series - Manual (Page 101)

Px Series Application Switch Installation and Configuration Guide 9-3
Health Checking Procedure
Health Checking Procedure
You configure health checks for each server group. All the members of a given server
group have the same health check performed on them. The health check process uses
the following procedure:
1 As soon as a server is enabled or the system comes up, a health check is performed
on the server. If it passes, the server goes up immediately
2 Health checks are performed at the configured interval .
— If a health check fails, it is retried at approximate intervals specified by
retry-interval , until it has failed fail-after times. Then the server is
removed from service.
— If the server passes a health check, it is retried at intervals specified by
retry-interval , until it passes restore-after times.
By default, interval is 30 seconds, retry-interval is 10 seconds, fail-after is 2
seconds, and restore-after is 2 seconds. You can change these default timer settings
locally on an individual server, or globally. If you set them globally, the timers are
modified on all hosts that use the default settings.
If health checks are enabled but not specifically configured, the default check is ping ,
with the default timer values. If the CPU is swamped by too many health checks or
other tasks, the times may stretch.
The TCP and HTTP health checks open a connection to the port configured for each
server in the server group. For HTTP health checks, you must specify the name of the
object to retrieve and a string to match, which must be a substring of the returned page.
After the connection is opened, the health check requests the specified object. If the
object is returned, the health check checks the first 1000 bytes of returned text to see if it
contains the string. If the string is found, the application is up and functioning.
Otherwise, the server fails the health check. If the server has failed too many times, it is
removed from the server group.
If you do not specify an object to retrieve, the health check does a “head /”. If anything
is returned, the check passes.
All data requests use HTTP 1.0.