How to keep the graph form when adding new arrows? - graphviz

Question

I have a graph like this:
Question 1: Is there a way to align the two columns horizontally in the top?
If I want to have an arrow a5 -> a1, then the graph would be:
Question 2: Is there a way to keep the graph as clean as before?
Here is the code:
digraph {
rankdir="LR";
// overlap=false;
nodesep="0.2";
ranksep="0.4";
fontsize = 25
labelloc="t";
fontname="Lato";
node [ shape="plaintext" style="filled, rounded" fontname="Lato" margin=0.2 ]
edge [ fontname="Lato" color="#2B303A" ]
subgraph cluster_0 {
style=filled;
color=lightgrey;
label = "Column 1";
fontsize = 20
node [style=filled,color=white];
a1
a2
a3
a4
a5
}
subgraph cluster_1 {
node [style=filled];
color=blue
label = "Column 2";
fontsize = 20
// labeljust=r
// labelloc=b
b1
b2
b3
b4
}
a1 -> b1
b1 -> a2
a2 -> b2
b2 -> a3
a3 -> b3
b3 -> a4
a4 -> b4
b4 -> a5
a5 -> a1
}

Answer 1

Two minor steps are needed:
(1) Put all a nodes in the same rank. If you don't, graphviz establishes a hierarchical relationship between a1 and a5, that's what your graph shows.
(2) Add some extra weight to the edge between a1 and b1, to keep it straight.
digraph {
rankdir="LR";
// overlap=false;
nodesep="0.2";
ranksep="0.4";
fontsize = 25
labelloc="t";
fontname="Lato";
node [ shape="plaintext" style="filled, rounded" fontname="Lato" margin=0.2 ]
edge [ fontname="Lato" color="#2B303A" ]
subgraph cluster_0 {
style=filled;
color=lightgrey;
label = "Column 1";
fontsize = 20
node [style=filled,color=white];
{rank = same; a1 a2 a3 a4 a5 } // !!!
}
subgraph cluster_1 {
node [style=filled];
color=blue
label = "Column 2";
fontsize = 20
// labeljust=r
// labelloc=b
b1
b2
b3
b4
}
a1 -> b1[ weight = 10 ]; // !!!
b1 -> a2
a2 -> b2
b2 -> a3
a3 -> b3
b3 -> a4
a4 -> b4
b4 -> a5
a5 -> a1
}
now produces

Answer 2

I'd go about this with the two following changes:
Use constraint=false in order to not have the edge from a5 to a1 mess up the graph
use the group attribute to suggest straight edges between nodes (same attribute value for nodes that should be placed in a straight line when connected with an edge)
digraph {
rankdir="LR";
// overlap=false;
nodesep="0.2";
ranksep="0.4";
fontsize = 25
labelloc="t";
fontname="Lato";
node [ shape="plaintext" style="filled, rounded" fontname="Lato" margin=0.2 ]
edge [ fontname="Lato" color="#2B303A" ]
subgraph cluster_0 {
style=filled;
color=lightgrey;
label = "Column 1";
fontsize = 20
node [style=filled,color=white];
a1 [group=1]
a2
a3
a4
a5
}
subgraph cluster_1 {
node [style=filled];
color=blue
label = "Column 2";
fontsize = 20
// labeljust=r
// labelloc=b
b1 [group=1]
b2
b3
b4
}
a1 -> b1
b1 -> a2
a2 -> b2
b2 -> a3
a3 -> b3
b3 -> a4
a4 -> b4
b4 -> a5
a5 -> a1 [constraint=false]
}