Customizing a monitors in F5 BIG-IP LTM

Customizing a monitor

The system provided monitors are used as templates for creating your own custom monitors.

A few monitors checks like ICMP can be used with little or no modification.

Most templates are just, templates. They are not designed to be used in production should be customized.

For example, many sites use the default HTTP monitor, but because it does not check content, it would not generally be recommended.

HTTP opens a connections sends a GET/ command and then marks the device ‘UP’ regardless of the content returned. With out user defined receive rule, the HTTP monitor will fail to detect many server problems.

There are also many templates that must be customized before they can be used. Many monitors checks require very specific information such as user name password, directory or database information, as well as an expected response.

Note that you can also use custom monitors as a template for creating other custom monitors.

Creating custom Monitors

General steps required to configure a new custom monitor.

1. To start, select monitors and then click the create button or select create from the flyout menu.
2. Note that the options on the monitors configuration screen very significantly depending on the type of monitor chosen.
3. In the general properties section, type the name for the custom monitor you are creating and then select a template from the type drop down menu.
4. In the configuration section enter appropriate settings for interval and time out.
5. For the HTTP monitor type, the send string is prepopulated with the GET/ command with no file name. this results in requests for the default webpage, such as index.html.

Additional monitor parameters

For some monitor types we can enter a regular expression for the regular string. The receive string causes BIG-IP to look for a match with in the service response before making the member ‘UP’.

The reverse receive rule will mark the member down, when the receive string response is found. This allows BIG-IP to check for down conditions like the server error-404page.

Monitor Timers

All monitors checks have an interval or frequency and timeout configuration settings.

The interval setting is the number of seconds between monitor checks, it determines the frequency BIG-IP will performed a monitor check on a node or pool member.

The timeout setting is also represented in seconds and determines how long to wait for a positive response before deciding to mark a pool member or node down. F5 networks recommends setting the timeout duration to 3 times the length of the interval setting, plus 1 additional second.

BIG-IP continues to issue monitor checks at the designated interval even if the node or pool member has been marked down. If the monitor check receives a positive response them the node or pool member status is changed to up or available.

.frequency of check (interval)

.timeout

    .recommended  : 3n+1