irule to force traffic to a particular server.

when CLIENT_ACCEPTED { 
  if { [IP::client_addr] == "10.20.1.111" } 
    { pool prod_443 member 10.9.41.25 } 
  elseif { [IP::client_addr] == "10.20.1.142" }
    { pool prod_443 member 10.19.41.24 } 
}

Your irule selects specific pool members for each client IP.

You need to check the status of the pool member with LB::status

when CLIENT_ACCEPTED { 
   get the default load-balancing pick
  set mypick [LB::select]
  if { (([IP::client_addr] == "10.20.1.111") && ([LB::status pool prod_443 member 10.9.41.25 443] eq "up"))  } 
    { pool prod_443 member 10.9.41.25 } 
  elseif { (([IP::client_addr] == "10.20.1.142") && ([LB::status pool prod_443 member 10.9.41.24 443] eq "up"))  }
    { pool prod_443 member 10.19.41.24 }
   the default pick is chosen 
  else { eval $mypick }
}

If i dont use the statement else { eval $mypick } will the default pool will not be selected or do i need specify the default pool member.

Yes - if you do not hit one of the explicit load-balancing selections, then the default load-balancing pool selection will occur.

I am having issues with this irule . It is not work at all. Can you please assist me on this

Rule [/Common/new_irule80] error: /Common/new_irule80:9: error: [undefined procedure: else][else { eval $mypick }]

and the traffic not hitting the irule at all.

Try the following:

when CLIENT_ACCEPTED { 
   get the default load-balancing pick
  set mypick [LB::select]
  if { (([IP::client_addr] == "10.20.1.111") && ([LB::status pool prod_443 member 10.9.41.25 443] eq "up"))  } { 
      pool prod_443 member 10.9.41.25 
  } 
  elseif { (([IP::client_addr] == "10.20.1.142") && ([LB::status pool prod_443 member 10.9.41.24 443] eq "up"))  } { 
      pool prod_443 member 10.19.41.24 
  } else {
       the default pick is chosen
      eval $mypick 
  }
}

Thankyou

but wondering apart from irule is there any other specific logic i can use as we have total 5 webseal servers ( all the client requests are being reverse proxied). So webseal servers are the one which is hitting the vip. So for now we are forcing 2 webseals to access the pool members directly and the othere 3 webseals are using the LB method( round robin) so the traffic atleast is distributed equally across 2 pool members.

Is there any better logic or method to setup the vip

I'm not sure I understand what you are trying to do.

using round robin and src IP persistence , 1 pool member is taking max hits so we want to reduce the connection overhead

so we cameup with the irule to limit 2 reverseproxy clients to access the pool members directly and the other 3 reverse proxy servers comes across round robin and src ip persistence.

I was wondering if there is a better way to implement this.