Fallback Host - Keep VIP URL

If you send a redirect to the client, the address bar will update with the new location. If you define the web-static.mysite.com server in a pool, you could check if the main www.mysite.com pool is down in CLIENT_ACCEPTED and select the web-static pool instead:

  
  when CLIENT_ACCEPTED {  
    
      Check if the VIP's default pool has no members up  
     if {[active_members [LB::server pool]] == 0}{  
    
         Select alternate pool  
        pool www-static.mysite.com_pool  
     }  
  }  
  

This will only check the pool state of the VIP's default pool when each client connects to the VIP. If you want to check on each HTTP -request you could move the pool checking to HTTP_REQUEST:

  
  when CLIENT_ACCEPTED {  
    
      Save the name of the VIP's default pool 
     set default_pool [LB::server pool]  
  }  
  when HTTP_REQUEST {  
    
      Check if the VIP's default pool has no members up  
     if {[active_members $default_pool] == 0}{  
    
         Select alternate pool  
        pool www-static.mysite.com_pool  
     }  
  }  
  

If you wanted to trigger this same logic when an individual load balancing attempt fails, you could add logic to the LB_FAILED event which checks 'if {[active_members $default_pool] == 0' and then calls LB::reselect to select www-static.mysite.com_pool. See the LB::reselect wiki page for details:

LB::reselect

http://devcentral.f5.com/wiki/default.aspx/iRules/lb__reselect

Aaron