Specifications

Chapter 6: Administering Virtual Clusters
84 Equalizer Installation and Administration Guide
Equalizer can perform the same exchange automatically and verify the server’s response by
checking the returned data against an expected result.
Specify an ACV probe string and an ACV response string to control the information that Equalizer
uses to perform the verification. Equalizer uses the probe string to request data from each server. To
verify the server’s content, Equalizer searches the returned data for the response string.
For example, you can use “
GET /index.html” as the ACV probe string and you can set the
response string to some text, such as “
Welcome” in the example in Figure 42, which appears on the
home page.
Similarly, if you have a Web server with a PHP application that accesses a database, you can use
ACV to ensure that all the components of the application are working. You could set up a PHP page
called test.php that accesses the database and returns a page containing “ALL OK” if there are no
problems.
Then you would enter the following values on the add cluster or modify cluster screens:
If the page that is returned contains the correct response string (in the first 1000 characters,
including headers) the server is marked “up”; if “ALL OK” were not present, the server is marked
down.
The response string should be text that appears only in a valid response. This string is case-
sensitive. An example of a poorly chosen string would be “HTML”, since most web servers
automatically generate error pages that contain valid HTML.
Enabling ACV
To enable ACV, follow these steps:
1. Log into the Equalizer Administration Interface in Edit mode.
2. In the left frame, click the name of the cluster to be configured. The cluster’s parameters appear
in the right frame.
3. Select Change Cluster Parameters from the local menu. The modify cluster screen opens in
the right frame.
4. In the ACV probe field, specify a non-empty string. Equalizer sends this string to each server
in the cluster to request verifiable data.
5. In the ACV response field, specify a case-sensitive string that is not empty. Equalizer uses this
string to verify the data with which the server responds to the ACV probe. For content
Note – When you set up a L7 cluster and add a probe string, \r\n (that is, a “carriage
return” followed by a “line feed”) is automatically added to the end of the string. On the other
hand, when you set up a L4 cluster and add a probe string, \r\n is not automatically added
to the end of the string. The reason for this different behavior is that L7 “knows” the protocol
is HTTP/HTTPS but L4 does not know the protocol to be used for the probe. If required for
an L4 cluster, these characters need to be added manually.