Hashing load balancing and persistence

The following is something I quickly wrote for a developer who wanted something simiiliar in that he wanted to the traffic to continue w/o having it "switch" when the faulty node came back up. This was written in v9.3.1 so I couldn't use the "active_members -list " command. This might exactly answer your question but it might help you think of solving your problem in a different way.

 
  This iRULE requires each pool have 1 member, and the last pool has all the combined members and it is equally balanced or prioritized. 
  The goal is when a client enters http://your.domain.com/?sid=P01 it will be directed to a specific pool.   
  If there is no URI, then look for a user-name in the http-header that that information and use CRC32 and create HASH number.   
  That number will be used to direct clients to a specific pool.  If there is no URI or user-name then do standard load balancing. 
  
 when HTTP_REQUEST { 
  This IF statement queries the URI to look for PO after a ? 
 if { [HTTP::query] contains "P0" } {  
  
  Takes the URI after ? skips 5 characters and sends the rest of the string to a variable. 
  For example, URI = /?sid=P01.  Looks at everything after ?, skips sid=P, scans the next 2 charcters/numbers  
  and sends the characters to the variable serverid. 
 set serverid [substr [HTTP::query] 5 2] 
  
  If another node is added to opentv, another pool statement must be added to the switch statement. 
 switch $serverid { 
 01 { pool pool_foobar.foo.com_01 } 
 02 { pool pool_foobar.foo.com_02 } 
 03 { pool pool_foobar.foo.com_03 } 
 04 { pool pool_foobar.foo.com_04 } 
 } 
 } 
 This statement checks to see if the is a user-name" 
 elseif { [HTTP::header exists "user-name"] } { 
  This creates a unique number using crc32 based on user-name in the http header and assigns it to a variable.  
  This unique number is passed to poolnum 
 set poolnum [crc32 [HTTP::header "user-name"]] 
  
  The following takes poolnum variable, divides it by 4 and assigns the remainder to poolnum.  
  This will result in the following answers 0,1,2,3.  If you divded by 5 then it's 0,1,2,3,4, etc,. 
  4 is equal to the total  of nodes in pool_foobar.foo.com_lb. 
  If a node is added then you must increment by N number of nodes that were added.   
  I.E., if 2 nodes are added then 4 + 2 = 6. 
 set poolnum [expr $poolnum % 4 ] 
  Increment the poolnum because we want a number higher then 0 to associate to a pool name. 
 incr poolnum 
  If another node is added to application, another pool statement must be added to the switch statement 
 switch $poolnum { 
 1 { pool pool_foobar.foo.com_01 } 
 2 { pool pool_foobar.foo.com_02 } 
 3 { pool pool_foobar.foo.com_03 } 
 4 { pool pool_foobar.foo.com_04 } 
      } 
 } 
 } 
  
  Triggered when the selected server fails in the selected pool, all connections on the failed node will be forced to reparticipate in load balancing. 
 when LB_FAILED {  
  if { [HTTP::header exists "user-name"] } { 
      set GOOD_NODES {} 
   When adding node then you must add the member node to NS 
      set NS {192.168.0.202 192.168.0.203 192.168.0.204 192.168.0.205} 
      foreach N $NS { 
         if { [LB::status pool pool_foobar.foo.com_lb member $N 8080] eq "up" } { 
            lappend GOOD_NODES $N 
         }       
      } 
    set NODENUM [crc32 [HTTP::header "user-name"]] 
    set NODENUM [expr $NODENUM % [active_members pool_foobar.foo.com_lb] ] 
    LB::reselect pool pool_foobar.foo.com_lb member [lindex $GOOD_NODES $NODENUM] 
    } 
    else {  
      pool pool_foobar.foo.com_lb 
      LB::reselect 
    } 
 } 
 

I hope this helps

CB