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Alteon Application Switch Operating System Application Guide
Health Checking
•
OFFSET (for binary content only)—Specify the offset from the beginning of the binary data area
to start matching the content specified in the EXPECT command. The OFFSET command is
supported for both UDP and TCP-based health checks. Specify the OFFSET command after an
EXPECT command if an offset is desired. If this command is not present, an offset of zero is
assumed.
•
DEPTH (for binary content only)—Specify the number of bytes in the IP packet that should be
examined. If no OFFSET value is specified, DEPTH is specified from the beginning of the packet.
If an OFFSET value is specified, the DEPTH counts the number of bytes starting from the offset
value.
•
WAIT—Specify a wait interval before the expected response is returned. The wait window
begins when the SEND string is sent from Alteon. If the expected response is received within the
window, the WAIT step passes. Otherwise, the health check fails. The WAIT command should
come after an EXPECT command in the script, or the OFFSET command if one exists after an
EXPECT command. The wait window is in units of milliseconds.
•
Wildcard character (*)—Trigger a match as long as a response is received from the server.
The wildcard character is allowed with the BEXPECT command, as in BEXPECT
OFFSET, or DEPTH commands that follow a wildcard character will be ignored.
Scripting Guidelines
•
Use generic result codes that are standard and defined by the RFC, as applicable. This helps
ensure that if the server software changes, the servers do not start failing unexpectedly.
•
Avoid tasks that may take a long time to perform or the health check will fail. For example, avoid
tasks that exceed the interval for load balancing.
Script Configuration Examples
This section includes the following script configuration examples:
•
Example 1: A Basic ASCII TCP-Based Health Check, page 498
•
Example 2: GSLB URL Health Check, page 499
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Example 3: A UDP-Based Health Check using Binary Content, page 500
•
Example 4: A TCP-Based Health Check using Binary Content, page 501
Example
1: A Basic ASCII TCP-Based Health Check
Configure Alteon to check a series of Web pages (HTML or dynamic CGI scripts) before it declares a
real server is available to receive requests.
498
. Any NEXPECT,
*
Document ID: RDWR-ALOS-V2900_AG1302
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