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C H A P T E R 18 Server Load Balancing (SLB)
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using the name and password supplied during the configuration.
The check will succeed when the switch successfully logs into the
next-hop.
Layer 7 NNTP Check
The NNTP health check connects to the server or next-hop,
establishes a connection, and attaches to a user defined newsgroup.
Layer 7 POP3, SMTP, and Telnet Check
These health checks attach to the server or next-hop using the
specified protocol and log in. After successful login the next-hop is
marked as up.
Internal Health Checking
Three types of internal health checks are available:
• Ping-check
• Port-check
• Service-check
If any of the health checks enabled on a given node do not pass
within the timeout specified, the node is considered down. When a
node is down, no new connection is established to that node until the
node passes all configured health checks. If a health check fails and
if the svcdown-reset parameter is enabled on an associated VIP
(virtual IP address), existing connections for the VIP on this node is
closed by sending TCP Reset to the client and node.
In the command-line interface, the commands
show pool and show
vip
display individual node resources as up or down. New
connections are only allowed if the VIP and node in question are
both enabled and up. A node is assumed to be up unless health
check is enabled and fails, in which case the node is marked down.
A resource is also marked down if it was disabled and the number
of existing connections drops to zero. If a node is marked down for
this reason, ping-checks and port-checks on this node are
automatically stopped to conserve system resources, but they
resume if the node is enabled by the user.