digraph cluster_arch {
    graph [center,
        //epsilon=0.1,
        label="Architecture Diagram for My Firefox Cluster",
        dpi=110, fontname="consolas"];
    edge [color=red, dir=both, fontsize="13", fontcolor="#666666"];
    node [fillcolor="#f5f694", color="white",style=filled, fontname="consolas"];

    firefox [label="Firefox farm"];
    apache [label="HTTP proxy (with cache) cluster"];
    prefetcher [label="Prefetcher cluster"];
    openresty [label="OpenResty cluster"];

    firefox ->  apache [label="HTTP proxy",len=3.2];
    prefetcher -> openresty [label="task fetch/submit",len=2.8];
    apache -> prefetcher [label="HTTP proxy",len=2];
    openresty -> firefox [label="task fetch/submit",len=3.2];
}