Fault Tolerant long-lived TCP connections

Hi David,

It sounds like you want to reselect a new pool member if the serverside connection is closed before the clientside connection is.

As you found, a health monitor and the 'action on service down' pool setting would happen too late to have any reliable effect on a single TCP connection.

Ideally, you'd be able to use an iRule which calls LB::reselect from the SERVER_CLOSED event. However, I'm not sure this is supported or would work. The wiki page for the SERVER_CLOSED event (Click here) doesn't show much hope as the LB::reselect command isn't listed there. A quick test shows the syntax parser doesn't allow it. And when you bypass the parser, it doesn't seem to work. Here is an apparently non-working example:

 
 when CLIENT_ACCEPTED { 
  
     Try to reselect a server 
    set reselect 1 
    log local0. "[IP::client_addr]:[TCP::client_port]: New connection to [IP::local_addr]:[TCP::local_port]" 
 } 
 when LB_SELECTED { 
    log local0. "[IP::client_addr]:[TCP::client_port]: Selected server info: [LB::server]" 
 } 
 when SERVER_CONNECTED { 
    log local0. "[IP::client_addr]:[TCP::client_port]: Connected server info: [IP::server_addr]:[TCP::server_port]" 
 } 
 when SERVER_CLOSED { 
  
    log local0. "[IP::client_addr]:[TCP::client_port]: Server connection closed" 
  
    if {$reselect}{ 
       log local0. "[IP::client_addr]:[TCP::client_port]: Trying reselect" 
       set lb_cmd "LB::reselect" 
       eval $lb_cmd 
    } 
 } 
 when CLIENT_CLOSED { 
  
     Do not try to reselect a server if the client closed the connection first 
    set reselect 0 
    log local0. "[IP::client_addr]:[TCP::client_port]: Client connection closed" 
 } 
 

Assuming this won't work, the best I can think of are ways to reduce the chance that LTM will close an idle connection. These configuration options are related to idle timeouts on the TCP and SNAT profiles:

SOL7606: Overview of BIG-IP LTM idle session timeouts

https://support.f5.com/kb/en-us/solutions/public/7000/600/sol7606.html

Aaron