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cgwin12's avatar
cgwin12
Icon for Altocumulus rankAltocumulus
Jan 05, 2026
Solved

error code 503 redirect irule

Hello, I want to create a logical path in F5 where if one server pool is down, we get an error code 503, then a redirect happens to a second pool. This is what I have written, but does not seem to re...
application delivery
management
  • cgwin12's avatar
    cgwin12
    Jan 08, 2026

    Injeyan, thanks for reaching out with your help. I wanted to share that we got this to work and I wanted to show how. 

     

    I applied this i-rule intially; 

     

    when HTTP_REQUEST {

    if { [HTTP::uri] contains "/pssmetrics" }{

    pool web-lb-dev-f5-ssl-pool2

    } else {

    pool web-lb-dev-f5-ssl-pool

    }

    }

    That specifies I want that uri to go to pool2. In pool 2 I have server 1 and server 2. Pool (1) only has server 1. Within pool2, I have a custom healh monitor, and when you mentioned a health monitor, that got me thinking along that track. Within the custom monitor, the pool member with the active service for pssmetrics will get the traffic load balanced to it, the condition being anytime there is a 503 error code. 

     

    So as  follows; 

    Send String:

    GET /pssmetrics HTTP/1.1\r\nHost: webfrontendalias.domain.org\r\nConnection: Close\r\n\r\n

    Receive String:

    302 

    (No OK after this, the regex gets cranky)

     

    Receive Disable Strng:

     

    503

     

cgwin12's avatar
cgwin12
Icon for Altocumulus rankAltocumulus
Jan 06, 2026

I thank you for this feedback. I need to include another detail. We have a situation where the pools will be up, but a specific application will be up on one pool and down on another. For example, https://webserver/pssmetrics may serve on pool 2, but not pool 1. If I get a 503 error code on pool 1 (the default), I want to failover to pool 2. I had an irule to look point to a pool based off uri. It won;t work for our purposes, but gives you an idea of how  I want to redirect. 

 

when HTTP_REQUEST {
  if { [HTTP::uri] contains "/pssmetrics" }{
    pool ta55-web-lb-dev-f5-ssl-pool2 
    } else {
    pool ta55-web-lb-dev-f5-ssl-pool 
  }
}

  • Injeyan_Kostas's avatar
    Injeyan_Kostas
    Icon for Nacreous rankNacreous
    Jan 06, 2026

    The approach is still the same 

    In your case you should just treat the specific path as unique application, meaning a dedicated pool with a specific health monitor. So the monitor is the one that will catch the 503 response beforehand.

    If you wait to check the response to the clint it's already too late 

    when HTTP_REQUEST {
  if { [HTTP::uri] contains "/pssmetrics" }{
   if { [active_members ta55-web-lb-dev-f5-ssl-pool2] > 0 } {
        pool ta55-web-lb-dev-f5-ssl-pool2 
      } else {
      pool ta55-web-lb-dev-f5-ssl-pool 
    }
  }
}