Layout in Graphviz

Question

The essential question is how to control the vertical and horizontal positioning of elements in Graphviz diagrams.

Consider this excerpt of a diagram (created in wysiwig editor).

I was trying to reproduce it in Graphviz to figure out whether it is suitable for my purposes.

digraph G {
compound=true;
node [shape=box];
edge [dir=none];
    subgraph cluster_tmk_web6 {
        nginx [label="nginx-frontend TCP 0.0.0.0:80"];

        subgraph clusteradminapp {
            unicorn [label="unicorn_rails TCP 127.0.0.1:8080"];
            subgraph clusterROR {
            label="ROR v.2.1";
            brida [label="brida_face_client"];
            }
            label="Admin App";
        }

        memcached [label="memcached"];
        sphinx;
        mongodb;

        subgraph cluster_errbit {
            unicorn2;
            ror3;
        }

    label="tmk-web6.service.home";
    }       

nginx -> unicorn;
memcached -> brida [lhead=clusterROR];


}

And the result goes like

I omitted some of the arrows, but the positioning is crucial for me. How do I move 'memcached' and 'sphinx' to the bottom of the cluster? How to shift 'mongodb' to the right? And finally, the diagram will consist of some 6 to 10 clusters of this size. How do I control the layout, placing some clusters in a row and others — above and below? I guess I should use "rank" attribute here, but not sure how. Please, help.

Answer 1

Just by adding the remaining edges (and two invisible edges), the graphviz output comes closer to your desired result:

digraph G {
compound=true;
node [shape=box];
edge [dir=none];
    subgraph cluster_tmk_web6 {
        nginx [label="nginx-frontend TCP 0.0.0.0:80"];

        subgraph clusteradminapp {
            unicorn [label="unicorn_rails TCP 127.0.0.1:8080"];
            subgraph clusterROR {
            label="ROR v.2.1";
            brida [label="brida_face_client"];
            }
            unicorn -> brida[style=invis];
            label="Admin App";
        }

        memcached [label="memcached"];
        sphinx;
        mongodb;

        subgraph cluster_errbit {
            unicorn2;
            ror3;
            unicorn2 -> ror3[style="invis"];
            label="Errbit";
        }

    label="tmk-web6.service.home";
    }       

nginx -> unicorn;
nginx -> unicorn2;
brida -> memcached [lhead=clusterROR];
brida -> sphinx [lhead=clusterROR];
ror3 -> mongodb;
}

Add some colors etc., and you're almost there.

But keep in mind, Graphviz is not a wysiwyg tool - its strong point is the automatic layout of nodes.