Respond with 5xx message when pool members connection limits reached (iRule?)

Have you tried using "Fallback Host" within the HTTP profile ? When a connection limit is reached, this will come into play.

You can also try LB_FAILED event:

when LB_FAILED {

}

Hi Roy,

if the connection limit of a pool member has been exhausted, the pool member will become temporary marked down, so that it does not receive any new connections attemps. During this time

[active_members]

do not count nor list the pool member which connection limit is exhausted.

You may try the iRule below. It performs a transparent

LB::reselect

in the case a pool member has just become unresponsive (but still marked as online) and also displays a

[HTTP::response 503]

in the case, that all remaining pool members are offline (or having their connection limits exhausted).

when LB_FAILED {
    if { not [info exists "reselect_count"] } then {
        set reselect_count 0
    }
    if { [active_members [LB::server pool]] > $reselect_count } then {
        LB::mode rr
        LB::reselect
        incr reselect_count
    } else {
        HTTP::respond 503 content "The application is too busy to serve your requests..."
        set reselect_count 0
    }
}

Cheers, Kai

Changed the iRule to be v11-compliant

when RULE_INIT {
        Set a global max for number of concurrent TCP connections
    set static::max_connections 2
     Set an HTML response to sent to clients who make a request while the VIP is over the max      connection count
    set static::html_content "over limit"

     Print debug messages to /var/log/ltm?  1=yes, 0=no
    set static::debug 1

     Initialize a counter for active connections (don't modify this)
    set static::active_connections 0
    }
    when HTTP_REQUEST {

     If we're over the limit for this connection, send a response
    if {$static::active_connections > $static::max_connections}{

     Send a response
    HTTP::respond 200 content $static::html_content

     Close the connection
    TCP::close

     Log a message to /var/log/ltm if debug is enabled
    if {$static::debug}{log local0. "Over limit (current/max:               $static::active_connections/$static::max_connections). Sent response to [IP::client_addr]"}

     We're not over the limit, so check if this is the first HTTP request on the TCP connection.  
    } elseif {[HTTP::request_num] == 1}{
      set validrequest 1
       Increment the TCP connection count.
      incr static::active_connections 1
    }
 }

when CLIENT_CLOSED {
    A connection was closed, so decrement the global counter
   if {$validrequest == 1}{
       incr static::active_connections -1
   }
}