When the proxy accepts a connection from a MySQL client, the connect_server() function is called.

There are no arguments to the function, but you can use and if necessary manipulate the information in the proxy.connection table, which is unique to each client session.

For example, if you have multiple backend servers then you can set the server to be used by that connection by setting the value of proxy.connection.backend_ndx to a valid server number. The code below will choose between two servers based on whether the current time in minutes is odd or even:

function connect_server()
        print("--> a client really wants to talk to a server")
        if (tonumber(os.date("%M")) % 2 == 0) then
                proxy.connection.backend_ndx = 2
                print("Choosing backend 2")
        else
                proxy.connection.backend_ndx = 1
                print("Choosing backend 1")
        end
        print("Using " .. proxy.global.backends[proxy.connection.backend_ndx].dst.name)
end

In this example the IP address/port combination is also displayed by accessing the information from the internal proxy.global.backends table.