irule

In that case I'd like to forward all requests to second server which is up. But I have a feeling that with this iRule client with ip 192.168.1.2 will be forwarded anyway to server1 which is down. Am I right ? And if yes how to avoid this situation ?

you may check pool member/node status before forwarding traffic.

LB::status

https://devcentral.f5.com/wiki/iRules.LB__status.ashx

In that case I'd like to forward all requests to second server which is up. But I have a feeling that with this iRule client with ip 192.168.1.2 will be forwarded anyway to server1 which is down. Am I right ? And if yes how to avoid this situation ?

you may check pool member/node status before forwarding traffic.

LB::status

https://devcentral.f5.com/wiki/iRules.LB__status.ashx

great, thanks so it will looks like this:

when HTTP_REQUEST { 

if { [LB::status pool $poolname member $ip $port] eq "up" && [LB::status pool $poolname member $ip2 $port] eq "up" } {
  if { [IP::addr [IP::client_addr] equals $client] } { 
       pool $poolname member $ip $port
     }
        elseif  { [IP::addr [IP::client_addr] equals $client2] } { 
                pool $poolname member $ip2 $port
                }  
 }
}

you can use active_members to check number of active pool members.

active_members

Or perhaps something like this:

when HTTP_REQUEST {
    if { ( [IP::addr [IP::client_addr] equals 192.168.1.2] ) and [LB::status pool Pool1 member 10.10.10.2 80] eq "up" ) } { 
        pool Pool1 member 10.10.10.2 80 
    } elseif  { ( [IP::addr [IP::client_addr] equals 192.168.1.3] ) and [LB::status pool Pool1 member 10.10.10.3 80] eq "up" ) } { 
        pool Pool1 member 10.10.10.3 80
    } else {
         not technically necessary if the pool is assigned to the VIP
        pool pool Pool1
    } 
}

This basically says, if the client source is this, and the specific pool member is up, then go ahead and send it. Otherwise send the request to whoever is available in the (default) pool.

uf, lot of options - I like it :)

Thank you guys