Configuring a Cluster’s Load-Balancing Options
Equalizer Installation and Administration Guide
135
Figure 28 Retrieving content from a server via telnet.
Equalizer can perform the same exchange automatically and verify the server’s response by checking the returned
data against an expected result.
Specifying an
ACV probe string
and an
ACV response string
basically automates the above exchange
.
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 28, 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.
For more information on probing, see “Server Health Check Probes and Timeouts” on page 265.
Enabling ACV
To enable ACV in an HTTP, HTTPS, or TCP cluster, follow these steps:
1. Log into the Administrative Interface using a login that has
add/del
access for the cluster (see “Logging In” on
page 52).
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 the
Probes
tab in the right frame.
4. In the
ACV probe
field, specify the string Equalizer will send to the server’s probe port; this string should cause
the application on the server’s probe port to respond with a string that contains the ACV response. Many
protocols require a string to be sent to the server before a response is received. Some protocols, such as SSH, do
not require a probe string; for such protocols, the ACV probe can be left blank.
> telnet www.myserver.com 80
Connected to www.myserver.com
> GET /index.html
<HTML>
<TITLE>Welcome to our Home Page</TITLE>
</HTML>
Connection closed by foreign host.
User requests connection to server.
Telnet indicates connection is established.
User sends request for HTML page.
Server responds with requested page.
Telnet indicates server connection closed.
Summary of Contents for E350GX
Page 18: ...Chapter Preface 18 Equalizer Installation and Administration Guide ...
Page 38: ...Chapter 1 Equalizer Overview 38 Equalizer Installation and Administration Guide ...
Page 80: ...Chapter 4 Equalizer Network Configuration 80 Equalizer Installation and Administration Guide ...
Page 110: ...Chapter 5 Configuring Equalizer Operation 110 Equalizer Installation and Administration Guide ...
Page 208: ...Chapter 7 Monitoring Equalizer Operation 208 Equalizer Installation and Administration Guide ...
Page 240: ...Chapter 8 Using Match Rules 238 Equalizer Installation and Administration Guide ...
Page 262: ...Appendix A Server Agent Probes 258 Equalizer Installation and Administration Guide ...
Page 274: ...Appendix B Timeout Configuration 270 Equalizer Installation and Administration Guide ...
Page 280: ...Appendix D Regular Expression Format 276 Equalizer Installation and Administration Guide ...
Page 310: ...Appendix F Equalizer VLB 306 Equalizer Installation and Administration Guide ...
Page 318: ...Appendix G Troubleshooting 314 Equalizer Installation and Administration Guide ...