example.dot

digraph G {
    ///// start Heroku styles
    graph [fontname="helvetica",fontsize=14,splines=true,pad=0.1,compound=true,color="grey60",fontcolor="grey10",fillcolor=grey95,style="filled"];
    node [fontname="helvetica",fontsize=12,color=purple4,shape=box,style="rounded, filled",fontcolor=purple4,fillcolor=grey99,penwidth=2];
    edge [fontname="helvetica",color=grey35,fontcolor=black,arrowhead="normal",penwidth=2,arrowsize=0.5];
    ///// end Heroku styles

    subgraph cluster3 {
      label="Common Runtime"
      "App C"
    }
    subgraph cluster1 {
      label="Private Space A"
      "App A"
      "Postgres Instance\n(Private or Shield Plan)"
    }
    subgraph cluster2 {
      label="Private Space B"
      "App B"
    }

    "App A" -> "Postgres Instance\n(Private or Shield Plan)" [color=chartreuse3]
    "App B":s -> "Postgres Instance\n(Private or Shield Plan)":ne [color=red, style=dashed, dir=none]
    "App C":s -> "Postgres Instance\n(Private or Shield Plan)":nw [color=red, style=dashed, dir=none]
}