Using F5 as a fall back host

At its most basic:

when RULE_INIT {
  set sorry "All Servers Down"
}
when HTTP_REQUEST {
  if {[active_members myPool] == 0} {
    HTTP::respond 200 content $::sorry
  }
}

If you do a little searching, I believe Hoolio posted an example with images...

Sounds like a good feature request. To make it officially, you could open a case with F5 support.

 

 

Aaron

You can accomplish the same thing as a backup pool by using priority within the pool. Just set the primary members (let's say there are three) with a higher priority than the backup nodes. Then set Minimum Active Members to 1, and if all 3 of the first priority group fail, the LTM will begin to use the backup node(s).

 

 

Denny

Hoolio,

 

 

Do you have the example with images handy? Guessing there is a specific Directory to put the image in and reference it in the html page string "

All Servers Down

 

" from the example from citizen_elah

 

 

Thanks,

 

 

Geoff

Hi Geoff,

 

 

Here you go: (Click here)

 

 

Aaron

Actually, I don't even use the RULE_INIT event. The entire response is an image:

class sorrypage {
   type string
   filename "/var/class/unavailable.class"
}
rule sorrypage-rule {
   when HTTP_REQUEST {
  if {[active_members http-pool] == 0} {
    HTTP::respond 200 content [b64decode [lindex $::sorrypage 0]] "Content-Type" "image/png"
  }
}
}

It's starting to - however the /error directory (and the if statement for the error_condition) is now confusing me - where does that /error supposed to exist?

I think I'm getting there following all your steps:

when RULE_INIT {
set ::polr_html {All Servers Down}
}
when HTTP_REQUEST {
if {[active_members myPool] == 0} 
if {$error_condition==1} {
 The error condition was true, so respond back to client from the iRule
 
switch [string tolower [HTTP::path]] {
/error/image.png {
HTTP::respond 200 content [b64decode [lindex $::logo_png_class 0]] "Content-Type" "image/png"}
default {
HTTP::respond 200 content $::polr_html
}
}
}

That's close. The /error/image.png only exists in the HTML you're sending to the client from the iRule. Can you give this a try?

I added some logging so you can check the /var/log/ltm log file for debug info if it doesn't work. You can check the file on the CLI using tail -f /var/log/ltm, (ctrl+c to stop tailing the file), or in the GUI under System >> Logs >> Local Traffic. Make sure to comment out the debug statements once you're done testing.

when RULE_INIT {
   set ::polr_html {All Servers Down}
}
when HTTP_REQUEST {
   log local0. "Received request from [IP::client_addr] to [HTTP::host][HTTP::uri], with [active_members myPool]"
    Check if the pool has any active members
   if {[active_members myPool] == 0}{
      log local0. "No active members"
       The error condition was true, so respond back to client from the iRule
      switch [string tolower [HTTP::path]] {
         /error/image.png {
            log local0. "Request was for /error/image.png"
            HTTP::respond 200 content [b64decode [lindex $::logo_png_class 0]] "Content-Type" "image/png"
         }
         default {
            log local0. "Request was not for the image, so we're sending the HTML"
            HTTP::respond 200 content $::polr_html
         }
      }
   }
}

Aaron

This works great! Thanks for all your help!

 

 

Geoff

One more question... can you run multiple iRules that reference "when HTTP_REQUEST" on the same Virtual Server or would you have to combine them into one iRule? I will need to have an iRule like the following example on the same VS:

when HTTP_REQUEST { 
      if {[HTTP::cookie exists "cookieName"]} { 
        HTTP::cookie decrypt "cookieName" "passphrase" 
      } 
  } 
   
  when HTTP_RESPONSE { 
      if {[HTTP::cookie exists "cookieName"]} { 
         HTTP::cookie encrypt "cookieName" "passphrase" 
      } 
  }

My guess is I would have to add in an elseif branch to the "if {[active_members myPool] == 0}{" to incorporate decrypting existing cookies within an HTTP Request.

Geoff