What could you do with your code in 20 Lines or Less? That's the question I ask (almost) every week for the devcentral community, and every week I go looking to find cool new examples that show just how flexible and powerful iRules can be without getting in over your head.

29 editions later and still going strong. The 20LoL is a testament to just how many different things can be done with iRules in just a few lines of code.  Just imagine the possibilities if this were the 30LoL.

This week I’ve got three more examples, all from the forums. Today we’ll cover dealing with port numbers in HTTP requests, checking pool status from within an iRule, and more fun with nested switching.  The community keeps putting out fantastic examples so I just keep on writing about them.  Keep it up.

 

Removing HTTP request port numbers

http://devcentral.f5.com/Default.aspx?tabid=53&forumid=5&postid=62227&view=topic

Hoolio came up with a trio if examples of how to deal with port numbers in your HTTP requests. All of them are good, depending on your situation, but I’m only going to highlight one here.  Go check out the forum post above to see the other two and get the context of the thread.

when HTTP_REQUEST {
  # Check if Host contains a colon
  if {[HTTP::host] contains ":"}{
    # Redirect client to requested host minus the port and preserve the original URI
    HTTP::redirect "
https://[getfield [HTTP::host] ":" 1][HTTP::uri]"
  }
}

 

Checking pool member status

http://devcentral.f5.com/Default.aspx?tabid=53&forumid=5&postid=62093&view=topic

User cmbhatt, another one of our power-users, came up with a very cool example of using the LB::select command and HTTP::respond to show the status of a selected pool member.  It even has a built in meta-refresh so you can continually monitor the status. Pretty neat stuff.

when HTTP_REQUEST {
     if {[HTTP::uri] eq "/status" } {
         scan [LB::select] %s%s%s%s%d command current_pool command2 current_member current_port
         eval [LB::select]
         set response "$current_pool Pool Status - [clock format [clock seconds]]http://[HTTP::host]/status'>"
         if { [active_members $current_pool] < 1 } {
             append response "POOL NAME:$current_pool
CURRENT MEMBER:$current_member:$current_port
STATUS: DOWN
"
         } else {
             append response "POOL NAME:$current_pool
CURRENT MEMBER:$current_member:$current_port
STATUS: UP
"
         }
     }
     HTTP::respond 200 content $response "Content-Type" "text/html"
}

 

More nested switching and pool selection vs. redirection

http://devcentral.f5.com/Default.aspx?tabid=53&forumid=5&view=topic&postid=62162

This rule stemmed from cmbhatt, once again, then I went in and made some tweaks where I think it made sense, as you can see in the thread.  The idea is that the user is looking to do some inspection of first the host, then in some cases, depending on what the host is, the URI as well.  Based on what’s found either a load balancing decision is made or a redirect is issued.  This is yet another awesome example of how iRules can turn something that would be ridiculously tricky or even impossible elsewhere into something pretty straight-forward.

when HTTP_REQUEST {
  switch [HTTP::host] { 
    "www.mydomain.eu" {
      switch [HTTP::uri] {
        "/" {  HTTP::respond 301 Location "
http://www.mydomain.eu/zz/index.html" }
        default { pool mydomain_eu_pool    }
      }
    }
    "www.mydomain.be" {
      switch [HTTP::uri] {
        "/" { HTTP::respond 301 Location "
http://www.mydomain.eu/be/zz/index.jsp" }
         default { pool mydomain_be_pool }
      }
    }
    "www.mydomain.nl" { HTTP::respond 301 Location "
http://www.mydomain.eu/nl/zz/index.jsp" }
    "www.mydomain.fr" -
    "mydomain.fr" { HTTP::respond 301 Location "
http://www.mydomain.eu/fr/zz/index.jsp }
    "www.mydomain.lu" { HTTP::respond 301 Location "
http://www.mydomain.eu/lu/zz" }
  }
}

 

There you have it, three more iRules to get you on your way in less than 21 lines of code.  Feel free to submit ideas, suggestions of feedback, as always.

#Colin