[%- level_1 = [];
    level_2 = [];
    level_3 = [];
    i = 0;
    WHILE i < 3;
        elem = 'FastCGI_' _ i;
        level_1.push(elem);
        i = i + 1;
    END;
    i = 0;
    WHILE i < 2;
        elem = 'proxy_' _ i;
        level_2.push(elem);
        i = i + 1;
    END;
    i = 0;
    WHILE i < 4;
        elem = 'Pg_' _ i;
        level_3.push(elem);
        i = i + 1;
    END;
%]
digraph cluster_arch {
    graph [K=0.8, center,
        label="OpenResty Cluster Architecture",
        dpi=110.0, fontname="consolas"];
    edge [color=red, dir=both, minlen=2];
    node [fillcolor=white, style=filled, fontname="consolas"];

    subgraph cluster_1 {
        graph [bgcolor="#ffdddd", label=""];
        node [label="FastCGI server"];
        [% FOREACH elem = level_1 %]
            [% elem %];
        [% END %]
    };

    subgraph cluster_2 {
        graph [bgcolor="#ddddff", label=""];
        node [label="PL/Proxy server"];
        [% FOREACH elem = level_2 %]
            [% elem %];
        [% END %]
    };

    [% FOREACH from = level_1 %]
        [% FOREACH to = level_2 %]
            [% from %] -> [% to %];
        [% END %]
    [% END %]

    subgraph cluster_3 {
        graph [bgcolor="#ddffdd", label=""];
        node [label="Pg node"];
        [% FOREACH elem = level_3 %]
            [% elem %];
        [% END %]
    };

    [% FOREACH from = level_2 %]
        [% FOREACH to = level_3 %]
            [% from %] -> [% to %];
        [% END %]
    [% END %]
}