node select iRule

e.g.

 config

root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm virtual bar
ltm virtual bar {
    destination 172.28.24.10:80
    ip-protocol tcp
    mask 255.255.255.255
    pool foo
    profiles {
        http { }
        tcp { }
    }
    rules {
        qux
    }
    source 0.0.0.0/0
    source-address-translation {
        type automap
    }
    vs-index 9
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm rule qux
ltm rule qux {
    when HTTP_REQUEST {
  set node_ip [getfield [HTTP::uri] "/" 4]
  log local0. "node_ip $node_ip"
  if { $node_ip >= 160 and $node_ip <= 253 } {
    HTTP::uri [string map [list $node_ip ""] [HTTP::uri]]
    log local0. "HTTP::uri [string map [list $node_ip ""] [HTTP::uri]] "
    log local0. "node 10.1.1.$node_ip 80"
  } else {
    log local0. "pool mediaroot-pool"
  }
}
}

 test

[root@ve11a:Active:In Sync] config  curl -I http://example.com/foo/bar/mediaroot/image1.jpg
HTTP/1.1 404 Not Found
Date: Tue, 29 Apr 2014 12:37:51 GMT
Server: Apache/2.2.3 (CentOS)
Content-Type: text/html; charset=iso-8859-1

[root@ve11a:Active:In Sync] config  tail /var/log/ltm
Apr 29 05:47:42 ve11a info tmm1[13022]: Rule /Common/qux : node_ip mediaroot
Apr 29 05:47:42 ve11a info tmm1[13022]: Rule /Common/qux : pool mediaroot-pool