Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 186)

170 Brocade Virtual ADX Server Load Balancing Guide
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Layer 7 health checks
4
HTTP (content verification)
The Brocade Virtual ADX sends HTTP GET or HEAD requests to HTTP servers when using SLB.
The GET or HEAD request specifies a page (identified by the URL) on the server. The Brocade Virtual
ADX examines the page and compares the contents of the page to a list of user-defined selection
criteria.
Based on the results of this comparison, the Brocade Virtual ADX takes one of the following actions
with respect to port 80 (HTTP) on the real server:
• If the page meets the criteria for keeping the port up, then the Brocade Virtual ADX marks the
port ACTIVE. This means that the HTTP application has passed the health check.
• If the page meets the criteria for bringing the port down, then the Brocade Virtual ADX marks
the port FAILED.
• If the page meets none of the selection criteria, then the Brocade Virtual ADX marks the port
either ACTIVE or FAILED according to a user-defined setting.
Refer to “Configuring HTTP content matching lists” on page 208 for information on specifying a
page to check and on setting up lists of selection criteria.
Performed:
• Immediately following a successful Layer 4 TCP health check
• At regular intervals, if keepalive is enabled for the port
Scripted (content verification for unknown ports)
After a successful Layer 4 health check, the Brocade Virtual ADX waits for the real server to send
back a packet in response.
The Brocade Virtual ADX looks in the response packet for a user-specified ASCII string, defined in a
matching list. The Brocade Virtual ADX compares the contents of the string to a list of user-defined
selection criteria in the matching list.
Based on the results of this comparison, the Brocade Virtual ADX takes one of the following actions
with respect to the port on the real server:
• If the text in the response meets the criteria for keeping the port up, then the Brocade Virtual
ADX marks the port ACTIVE.
• If the text in the response meets the criteria for bringing the port down, then the Brocade
Virtual ADX marks the port FAILED.
• If the text in the response meets none of the selection criteria, then the Brocade Virtual ADX
marks the port either ACTIVE or FAILED according to a user-defined setting.
• If no response is received within the configured interval (the default is five seconds), the
Brocade Virtual ADX sends a RST and retries the health check. After the configured number of
retries (the default is two retries), if the server still does not respond, the Brocade Virtual ADX
marks the server port FAILED.
Refer to “Configuring scripted health checks” on page 211 for more information.
Performed:
• Immediately following a successful Layer 4 TCP health check
• At regular intervals, if keepalive is enabled for the port