Placing clusters on the same rank in Graphviz

Question

I would like these two nodes to appear on the same level:

digraph G {
    subgraph cluster1 {
        label="Local Datacenter";
        router1;
        host1;
    }
    subgraph cluster2 {
        label="Remote Datacenter";
        router2;
        host2;
    }
    router1 -> router2;
    router2 -> host2;
    router1 -> host1;
}

I have tried using rank=same and rank=min, but they aren't giving me what I need.

Interestingly, if I set rankdir=LR and comment out the two router-to-host edges, it gives me exactly the look I want - but I would like to leave the edges intact.

Answer 1

You may use the newrank graph attribute (added in GraphViz 2.30) to activate the new ranking algorithm which allows defining rank=same for nodes which belong to clusters.

Add the following line at the top:

newrank=true;

Add the following line after the cluster definitions:

{ rank=same; router1; router2; }

Here's the resulting graph:

Answer 2

You may simply modify the edge between the routers:

router1 -> router2[constraint=false];

constraint indicates whether the edge should be used in the ranking of the nodes.