Draw subgraphs independently

[eyssette]

A solution would be to use ranksep=0.1 and change the len of specific edges, with minlen.

digraph G {
ranksep=0.1
    subgraph cluster_outer {
        subgraph cluster_1 {
            a [shape=rect, height=1.5]
            b [shape=rect]
            a -> b[minlen=2]
        }
        
        subgraph cluster_2 {
            
           c [shape=rect]
           d [shape=rect]
           c -> d [color=red]
           color=red
        }
    }
}