Forum Discussion
Sylvain_85827
Cirrus
CirrusRewrite URL based on selected node for load-balancing
Dears iRules Gurus and community,
Once again I need your help ^^ I'm wondering how to rewrite an URL of HTTP requests (IPP in fact) depending on the node chosen for load-balancing the traffic.
Typically in ASCII ART or RFC style this would give:
|| ----- if node1 selected for load-balancing -----> https://mynode1/xxxxxx ----> node 1 IIS server
https://mypublicurl/xxxxxx ----> || f5 LTM v11 || ----- if node2 selected for load-balancing -----> https://mynode2/xxxxxx ----> node 2 IIS server
|| ----- if node3 selected for load-balancing -----> https://mynode3/xxxxxx ----> node 3 IIS server
|| etc...
Any idea?
Thanks for your very valuable (and appreciated :D) help!
Cheers.
18 Replies
- Kevin_Stewart
Employee
I was going under the assumption that you wouldn't know the host value in the redirect, but yes this other method would work if you did know it. 
Sylvain_85827Hi,
it's me again 🙂 but this time only for giving you feedback.
@Kevin
I don't know why below code caught all the host name between https:// and the next / except the first letter!if { [scan $uri_old {%*[http://|https://]%[^/]} host_old] } {
So I changed it like this:if { [scan $uri_old {%[^//]//%[^/]]} host_tmp host_old] } {
Certainly not the best, but at least it is working 😄
Finally the iRule became:when RULE_INIT { Log debug messages to /var/log/ltm? 1=yes, 0=no set static::rewrite_debug 1 External hostname for the web application set static::external "mypublicsite.com" } when HTTP_REQUEST_SEND { Need to force the host header replacement and HTTP:: commands into the clientside context as the HTTP_REQUEST_SEND event is in the serverside context clientside { Different action depending on the node selected for load-balancing switch [LB::server addr] { "1.1.1.1" { HTTP::header replace Host "internalhost01.com" if {$static::rewrite_debug}{log local0. "[IP::client_addr]:[TCP::client_port]: HTTP Host header rewritten with internalhost01.com"} } "1.1.1.2" { HTTP::header replace Host "internalhost02.com" if {$static::rewrite_debug}{log local0. "[IP::client_addr]:[TCP::client_port]: HTTP Host header rewritten with internalhost02.com"} } } } } when HTTP_RESPONSE { Replace all internal Host headers with $static::external value defined in RULE_INIT section HTTP::header replace Host $static::external if {$static::rewrite_debug}{log local0. "[IP::client_addr]:[TCP::client_port]: HTTP Host header rewritten with -> $static::external"} if { [HTTP::is_redirect] } { Log if we detect an HTTP redirection if {$static::rewrite_debug}{log local0. "[IP::client_addr]:[TCP::client_port]: HTTP redirection detected"} Store Location HTTP header coming from backend server set uri_old [string tolower [HTTP::header Location]] Store backend server host name if { [scan $uri_old {%[^//]//%[^/]]} host_tmp host_old] } { Replace backend server host name with external host name into HTTP Location header set map_exp "set uri_new \[string map {$host_old $static::external} $uri_old\]" eval $map_exp Finally rewrite HTTP Location header HTTP::header replace Location $uri_new if {$static::rewrite_debug}{log local0. "[IP::client_addr]:[TCP::client_port]: HTTP Location header rewritten with -> $uri_new"} } } }
I sincerely thank you all for your very valuable help! Without you this story would have taken me too much time, really thank you.- nitass
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- Sylvain_85827Posted By nitass on 07/10/2013 06:35 AM
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Can't read your reply sorry... - Sylvain_85827
Got it in my email but I'm really not sure about what you replied exactly, can you please explain nitass?
- nitassI don't know why below code caught all the host name between https:// and the next / except the first letter!i understand square brackets treat thing inside as character rather than word. for example, [https] means h, t, p and s characters. so, if hostname starts with one of them, it will be included.
tcl scan
[chars]
The input substring consists of one or more characters in chars. The matching string is stored in the variable. If the first character between the brackets is a ] then it is treated as part of chars rather than the closing bracket for the set. If chars contains a sequence of the form a-b then any character between a and b (inclusive) will match. If the first or last character between the brackets is a -, then it is treated as part of chars rather than indicating a range.% set uri_old "http://some.domain.com/something" http://some.domain.com/something % scan $uri_old {%*[http://|https://]%[^/]} host_old 1 % put $host_old ome.domain.com - Kevin_StewartSlight variation:
scan $uri_old {%*[^/]//%[^/]} host_old - Sylvain_85827Thank you all for your help! I learn so much with you and have a lot of fun by the way ^^
