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Requirement:
Translate HTTP Host header value with pattern matching when forwarding client’s request to real server pool.
Client Request -> FortiADC VS:
https://fadc-uat.lab.local
FortiADC VS -> real server pool:
https://fadc-uat-int.lab.local
- Create Scripting under Server Load Balance -> Scripting -> Create New.
a. Define name.
b. Input Lua script statement.
c. Select Save.
when HTTP_REQUEST {
-- Get the Host header
hostname = HTTP:header_get_value("Host")
debug("Original HTTP host is: %s\n", hostname)
-- Perform pattern check using regex
local match_result = string.match(hostname, "^fadc%-(.*)%.lab%.local$")
if match_result then
-- format of string.gsub(input, pattern, replacement) / "%1" in replacement is back-reference for call group in pattern
new_host = string.gsub(hostname, "^fadc%-(.*)%.lab%.local$", "fadc-%1-int.lab.local")
-- debug print to help troubleshoot issues with string/pattern matching
debug("New HTTP host is: %s\n", new_host)
-- Replace HTTP Host with new string replacement
HTTP:header_replace("Host", new_host)
LB:routing("DVWA_CR")
else
-- print as such if nothing is matched
debug("HTTP Host did not match the pattern.\n")
end
}
Details and comments of the Lua script used in this article:
- Assign a virtual server with the created script under Server Load Balance -> Virtual Server, edit the respective virtual server, enable Scripting, and select the created script:
Demonstration:
• Simulate request to FortiADC virtual server e.g https://fadc-uat.lab.local/login.php
• Expect script to replace HTTP host when forwarding the request to the real server pool.
SLB traffic log: Client request to FortiADC virtual server
Packet capture: Client request forwarded to real server – HTTP host is replaced with a new value
Note:
In this demonstration, only the request HTTP Host is translated/replaced.
Debugging commands for troubleshooting:
diagnose debug module httproxy scripting set
diagnose debug module httproxy scripting_minor set
diagnose debug enable
Disabling debugging output:
diagnose debug disable
diagnose debug module httproxy all unset
Related document:
FortiADC - HTTP Scripting
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