Installation guide

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Device Manager Guide, Cisco ACE 4700 Series Application Control Engine Appliance
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Chapter 6 Configuring Real Servers and Server Farms
Configuring Health Monitoring
The ACE appliance sends out probes periodically to determine the status of a server, verifies the server
response, and checks for other network problems that may prevent a client from reaching a server. Based
on the server response, the ACE appliance can place the server in or out of service, and, based on the
status of the servers in the server farm, can make reliable load-balancing decisions.
Health monitoring on the ACE appliance tracks the state of a server by sending out probes. Also referred
to as out-of-band health monitoring, the ACE appliance verifies the server response or checks for any
network problems that can prevent a client to reach a server. Based on the server response, the ACE
appliance can place the server in or out of service, and can make reliable load balancing decisions.
Note You can configure the inband health monitoring feature and health probes to monitor the health of the
real servers in a server farm. For more information on inband health monitoring, see the “Configuring
Server Farms” section on page 6-18.
The ACE appliance identifies the health of a server in the following categories:
• Passed—The server returns a valid response.
• Failed—The server fails to provide a valid response to the ACE or the ACE is unable to reach a
server for a specified number of retries.
By configuring the ACE appliance for health monitoring, the ACE appliance sends active probes
periodically to determine the server state.
The ACE appliance supports 4000 unique probe configurations which includes ICMP, TCP, HTTP, and
other predefined health probes. The ACE appliance also allows the opening of 1000 sockets
simultaneously.
Related Topics
• Configuring Health Monitoring for Real Servers, page 6-41
• TCL Scripts, page 6-40
TCL Scripts
The ACE appliance supports several specific types of health probes (for example HTTP, TCP, or ICMP
health probes) when you need to use a diverse set of applications and health probes to administer your
network. The basic health probe types supported in the current ACE appliance software release may not
support the specific probing behavior that your network requires. To support a more flexible
health-probing functionality, the ACE appliance allows you to upload and execute TCL scripts on the
ACE appliance.
The TCL interpreter code in the ACE appliance is based on Release 8.44 of the standard TCL
distribution. You can create a script to configure health probes. Script probes operate similar to other
health probes available in the ACE appliance software. As part of a script probe, the ACE appliance
executes the script periodically, and the exit code that is returned by the executing script indicates the
relative health and availability of specific real servers. For information on health probes, see
Configuring Health Monitoring for Real Servers, page 6-41.
For your convenience, the following sample scripts for the ACE appliance are available to support the
TCL feature and are supported by Cisco TAC:
• ECHO_PROBE_SCRIPT
• FINGER_PROBE_SCRIPT
• FTP_PROBE_SCRIPT