Fail Detection

It is important for TWCB to know whether a cache server can provide the requested service. There are three fail detection methods for determining the state of a cache server, server port, and application content:

• Ping - The real server is pinged.
• TCP 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 cache server occurs by default, using the predefined ICMP probe $twcb_default. See Preset Default ICMP Probes for preset default ICMP probe details.

TWCB supports the assigning of up to two probes per server: an ICMP ping and a TCP or UDP probe that can be configured for port verification and optionally for ACV. Probes are assigned to a cache server configuration using the faildetect probe command in cache server configuration mode. When assigning a probe to a cache server, specify probe one or two, and the name of the probe. The $twcb_default default ICMP ping probe is auto-assigned to probe one.

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. 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 $twcb_default default probe for the server context
• Removes any configured probe configuration for probe two

TWCB fail detection sets the application port to 80 by default. Use the faildetect app-port command in cache server configuration mode to set the TCP port on the cache server to a value other than 80 if required.

Any preexisting probe is overwritten when assigning a probe.

This example shows how to:

• Create a TCP probe named TCP-HTTP
• 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 186.89.10.51 cache server on the TWCB server farm s1Server:
• Assign port 8080 as the TCP port to be monitored.
• Enable the real server configuration

  System(su)->configure
  System(su-config)->probe TCP-HTTP tcp
  System(su-config-probe)->inservice
  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)->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 twcb wcserverfarm s1Server
  System(config-twcb-wcsfarm)->cache 186.89.10.51
  System(config-twcb-cache)->faildetect probe one TCP-HTTP
  System(config-twcb-cache)->faildetect app-port 8080
  System(config-twcb-cache)->inservice
  System(config-twcb-cache)->