Fail Detection

It is important for LSNAT to know whether a real server can provide the requested service. There are three methods supported to determine the state of a real server, server ports, and its applications:

• Ping - The real server is pinged.
• TCP/UDP Port Service Verification - The application service port is verified.
• Application Content Verification (ACV) - The content of an application is verified.

Fail detection methods are configured within probes using the tracked object manager facility. Probe creation and configuration is detailed, along with fail detection method details in Tracked Object Manager Configuration.

ICMP ping probe monitoring of a real server occurs by default, using the predefined ICMP probe $slb_default. See Preset Default ICMP Probes for preset default ICMP probe details.

LSNAT server load balancing supports the assigning of up to two probes per server: an ICMP ping and a UDP or TCP probe that can be configured for port verification and optionally for application content verification. Probes are assigned to a real server configuration using the faildetect probe command in real server configuration mode. When assigning a probe to a real server, specify probe one or two, and the name of the probe. The $slb_default default ICMP ping probe is auto-assigned to probe one, whenever probe one is not configured with an administratively created probe.

The probe type setting allows you to set whether configured probes are active or inactive for a server context. The probe type setting does not change the probe configuration. When probe type is set to probe, the probe configuration for the server context is active; probes are sent to the server in accordance with the configured settings. When probe type is set to none, the probe configuration is inactive; no probes are sent for the server context, and the real server is set to UP. The default probe type is probe. Use the probe type command in real server configuration mode to set the probe type for the server context.

In a server configuration context, probe configuration can be reset to factory default values by resetting fail detection for that server context. Resetting fail detection in a server configuration context:

• Sets the probe type to the default value of probe
• Sets the probe for probe one to the default probe for the server context
• Removes any configured probe configuration for probe two

Any preexisting probe is overwritten when assigning a probe.

This example shows how to:

• Create a TCP probe named TCP-HTTP
• Set the fail detection interval to 5 seconds
• Set the pass detection interval to 5 seconds
• Configure the ACV request and reply strings
• Place the probe inservice
• Display a detailed level of configuration information for the probe
• Assign the probe to probe one of the 10.1.2.3 port 80 real server in the server farm myproductHTTP:
• Enable the real server configuration

  System(su)->configure
  System(su-config)->probe TCP-HTTP tcp
  System(su-config-probe)->faildetect interval 5
  System(su-config-probe)->passdetect interval 5
  System(su-config-probe)->acv request “GET / HTTP/1.1\\r\\nHost: 2.0.0.5\\r\\n\\r\\n”
  System(su-config-probe)->acv reply “HTTP/1.1 200 OK\\r\\n”
  System(su-config-probe)->inservice
  System(su-config-probe)->show probe TCP-HTTP detail
  Probe:                        TCP-HTTP  Type:                           tcp-acv
  Administrative state:        inservice  Session count:                        1
  Fail-detect count:                   3  Pass-detect count:                    3
  Fail-detect interval:                5  Pass-detect interval:                 5
  3-way TCP handshake wait time:       5  Server response wait time:           10
  Application Content Verification:
   Request-string: GET / HTTP/1.1\\r\\nHost: 2.0.0.5\\r\\n\\r\\n
   Reply-string:   HTTP/1.1 200 OK\\r\\n
   Close-string:
   Search-Depth:   255
  System(su-config-probe)->exit
  System(su-config)->ip slb serverfarm myproductHTTP
  System(su-config-slb-sfarm)->real 10.1.2.3 port 80
  System(su-config-slb-real)->faildetect probe one TCP-HTTP
  System(su-config-slb-real)->inservice
  System(su-config-slb-real)->