Using F5 as a fall back host

 
  when RULE_INIT { 
      
      maint_prefix must not contain a trailing slash 
      maint_prefix also must not exist on your real web servers 
      
     set maint_prefix "/maintenancepage" 
     set maint_len [string length $maint_prefix] 
   } 
   when HTTP_REQUEST { 
      
      Service requests for files (URIs) from the maintenance page 
      Note that we always service these pages, even if the http_pool is up 
      
     set uri [HTTP::uri] 
     if { $uri equals ${::maint_prefix} } { 
        HTTP::respond 301 "Location" "${::maint_prefix}/" 
        return 
     } 
     if { $uri starts_with "${::maint_prefix}/" } { 
         trim off the maintenance prefix 
        set uri [string range $uri $::maint_len end] 
  
         Return the requested page 
        switch $uri { 
          "/"              - 
          "/index.html"   { HTTP::respond 200 content [lindex $::maint_index_html 0]           "Content-Type" "text/html" } 
          "/logo.png"     { HTTP::respond 200 content [b64decode [lindex $::maint_logo_png 0]] "Content-Type" "image/png" } 
          default         { HTTP::respond 404 } 
        } 
        return 
     } 
  
      
      If the http_pool is down, redirect to the maintenance page 
      
     if { [active_members http_pool] < 1 } { 
       HTTP::redirect "${::maint_prefix}/index.html" 
       return 
     } 
   }