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Health monitors

BIG-IP® Reference Guide 4 - 137

Health monitors

Health monitors verify connections and services on nodes that are members

of load balancing pools. The monitor checks the node at a set interval. If the

node does not respond within a specified timeout period, the node is marked

down and traffic is no longer directed to it.

By default, an icmp (Internet Control Message Protocol) monitor is

associated with every node that is a member of a load balancing pool. This

monitor is of the simplest type, checking only the node address and

checking only for a ping response. To change the interval and timeout

values of this default check, or to check specific services on a node, you

need to configure a custom monitor or monitors to add to the default

monitor. The BIG-IP provides a variety of service-specific monitors in

template form. Some of these monitors are usable as is (assuming their

default values are acceptable) and may be put in service simply by

associating them with the nodes to be monitored. In most cases, however,

the template is used purely as a template for configuring custom monitors.

Configuring custom monitors and placing them in service is a three-step

process:

• Selecting the template

• Configuring the monitor from the template

• Associating the monitor with the node or nodes

For example, for the default icmp monitor, we selected the icmp monitor

template, as shown in Figure 4.51.

The icmp monitor template has three attributes, interval, timeout, and dest,

each with a default value. (All monitor templates have these three basic

attributes. Other monitor templates have additional attributes as required by

the service type.) These attributes are inherited by the custom monitor when

it is configured and can be left at their default values or assigned new values

as required.

For the default monitor, template icmp is used as is, that is, as monitor icmp

with its default attribute values. To change any of these default values, you

need to create a custom monitor based upon icmp, for example, my_icmp.

Only the values that are actually to be changed would need to be specified in

the definition of the custom monitor. Therefore, if you wanted to change the

timeout values only, you define the custom monitor as follows:

b monitor my_icmp ’{ use icmp timeout 20 }’

monitor type icmp {

interval 5

timeout 16

dest *

}

Figure 4.51 The icmp monitor template

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