box Client [line.radius=3, line.corner=bevel, line.width=2];
space;
box Processing [fill.color=aqua+80, line.radius=5] {
    chart signalling <<<
        background.color=none;
        hscale=auto;
        Server, LB [show=no], Backend1, Backend2;
        ->Server;
        show LB;
        Server->LB;
        LB->Backend2;
        hide LB;
        Backend2--Backend2:Proc;
        join <->:external\nreq;
        Server<-Backend2;
        <-Server;
    >>>;
};
space;
box zone: zone nw [line.type=dotted] {
    *def.db db [size=40, line.width=2, middle=Client];
    *def.db [size=40, line.width=2];
}
below +30 *def.actor op [size=20, color=orange];
below -10 text: \-Operator;
Client<=>Processing<=>db;
op=>zone: config [label.pos=middle];