User Manual

Enterasys X-Pedition User Reference Manual 345
Load Balancing
Verifying Extended Content
You can also have the X-Pedition verify the content of an application on one or more load
balancing servers. For this type of verification, you specify the following:
• A string that the X-Pedition sends to a single server or to the group of load balancing servers.
The string can be a simple HTTP command to get a specific HTML page. Or, it can be a
command to execute a user-defined CGI script that tests the operation of the application.
• The reply that the application on each server sends back that the X-Pedition will use to validate
the content. In the case where a specific HTML page is retrieved, the reply can be a string that
appears on the page, such as “OK.” If a CGI script is executed on the server, it should return a
specific response (for example, “OK”) that the X-Pedition can verify.
Application Content Verification (ACV) is a method of ensuring that data coming from your
servers remains intact and does not change without your knowledge. ACV can simultaneously
protect against server outages, accidental file modification or deletion, and servers whose security
has been compromised. By nature, ACV is protocol independent and is designed to work with any
type of server that communicates via formatted ASCII text messages, including HTTP, FTP, and
SMTP. ACV works by sending a command to your server and searching the response for a certain
string. If it finds the string, the server is marked as Up—if not, the server is marked as Down. For
example, if you sent the following string to your HTTP server, “GET /index.html
HTTP/1.1\r\nHost: <server IP>\r\n\r\n”, you could search for a response similar to the following
(this response would be an ETag in the packet's HTTP header):
Another approach is to use the “Last Modified” field of the HTTP header. Because ACV can search
for a string in only the first 255 bytes of the response, in most HTTP cases the response will have to
be in the packet's HTTP header (i.e., you will not be able to search for a string contained in the web
page itself). Some protocols such as FTP or SMTP require users to issue a command to close the
session after making the request. This command should appear in the acv-quit field.
Note: A Line Feed character “\n” is appended to these commands when they are sent to the
server; therefore, it is not necessary to put a CR or LF in your acv-quit string. For
example, when working with FTP, use “BYE” rather than “BYE\n.”
You can verify application content by entering the following Configure mode commands:
12345-123a-12345678
Specify application verification for
all servers in specified group.
load-balance set group-options <group name> acv-
command
<command string> acv-reply <reply
string>
read-till-index <reply string> [check-port
<port-number>][acv-quit <quit string>]
Specify application verification for
specified server.
load-balance set server-options <ipaddr> port <port
number>
acv-command <command string> acv-
reply
<reply string> read-till-index <reply string>
[check-port <port-number>][acv-quit <quit
string>
]