Sql sessions

You don't need an irule to set the maximum limit of concurrent connections to a pool member, instead you can edit the pool member properties and set the "Connection Limit" setting to your desired value. This is what the help says:

Connection Limit

Specifies a maximum established connection limit for a pool member or node. When the current connections count reaches this number, the system does not send additional connections to that pool member or node. The default is 0, meaning that there is no limit to the number of connections.

In addition, if the pool member reaches the connection limit, it will be marked in the GUI with a yellow triangle icon (instead of blue square or green circle) meaning that it is unavailable but may become available without user intervention.