i'm trying to set the size of the nodes this way:
controller[shape=circle,width=.5,label="Controller",style=filled,fillcolor="#8EC13A"];
But all three nodes are with different size. How can i set fixed size?
From the DOT Guide http://www.graphviz.org/pdf/dotguide.pdf on page 4 it says the following:
When drawn, a node’s actual size is the greater of the requested size and the area needed for its text label, unless fixedsize=true, in which case the width and height values are enforced.
Thus you simply need to add fixedsize=true to your code